2. Demonstrative pronouns ('I' means the instrumental case)
3. Interrogative pronouns
N hwá hwæt 
 G hwæs hwæs 
 D hwæ'm hwæ'm 
 A hwone hwæt 
 I - hwý, hwí
These pronouns, which actually mean the masculine and the neuter varieties of the same pronoun, derive from Proto-Indo-European *kwis, with *kw becoming hw in Germanic languages. In Gothic the combination hw was considered as one sound which is another proof that the Indo-European the labiovelar sound kw was a single sound with some specific articulation.
Later Germanic languages changed the sound in a different way: in Norwegian it remained as hv, in German turned into w (as in wer 'who', was 'what'), in English finally changed into wh pronounced in most cases [w], but somewhere also like [h] or [hw].
Interesting that the instrumental of the word hwæt, once being a pronoun form, later became the word why in English. So 'why?' is originally an instrumental case of the interrogative pronoun.
Other interrogative pronouns, or adverbs, as they are sometimes called, include the following, all beginning with hw:
hwilc 'which?' - is declined as the strong adjective (see adjectives above) 
hwonne 'when?' - this and following are not declined, naturally 
hwæ'r 'where?' 
hwider 'whither?' 
hwonan 'whence?'
4. Other kinds of pronouns
They include definite, indefinite, negative and relative, all typical for Indo-European languages. All of them still exist in Modern English, and all of them are given here:
a) definite 
gehwá (every) - declined the same way as hwá 
gehwilc (each), 
ægþer (either), 
æ'lc (each), 
swilc (such) - all declined like strong adjectives 
sé ylca (the same) - declined like a weak adjective
b) indefinite 
sum (some), 
æ'nig (any) - both behave the same way as strong adjectives
c) negative 
nán, næ'nig (no, none) - declined like strong adjectives
d) relative 
þe (which, that) 
séþe (which, that) - they are not declined
In Proto-Indo-European and in many ancient Indo-European languages there was a special kind of declension calleed pronominal, using only by pronouns and opposed to the one used by nouns, adjectives and numerals. Old English lost it, and its pronouns use all the same endings as the nouns and adjectives. Maybe the only inflection which remembers the Proto-language times, is the neuter nominative -t in hwæt and þæt, the ancient ending for inanimate (inactive) nouns and pronouns.
The Old English Numeral.
It is obvious that all Indo-European languages have the general trend of transformation
from the synthetic (or inflectional) stage to the analytic one. At least for the latest 1,000 years this trend could be observed in all branches of the family. The level of this analitization process in each single language can be estimated by several features, their presence or absence in the language. One of them is for sure the declension of the numerals. In Proto-Indo-European all numerals, both cardinal and ordinal, were declined, as they derived on a very ancient stage from nouns or adjectives, originally being a declined part of speech. There are still language groups within the family with decline their numerals: among them, Slavic and Baltic are the most typical samples. They practically did not suffer any influence of the analytic processes. But all other groups seem to have been influenced somehow. Ancient Italic and Hellenic languages left the declension only for the first four cardinal pronouns (from 1 to 4), the same with ancient Celtic.
The Old English language preserves this system of declension only for three numerals. It is therefore much easier to learn, though not for English speakers I guess - Modern English lacks declension at all.
Here is the list of the cardinal numerals: 
Ordinal numerals use the suffix -ta or -þa, etymologically a common Indo-European one (*-to-).
The Old English Adverb.
Adverbs can be either primary (original adverbs) or derive from the adjectives. In fact, adverbs appeared in the language rather late, and eraly Proto-Indo-European did not use them, but later some auxiliary nouns and pronouns losing their declension started to play the role of adverbial modifiers. That's how thew primary adverbs emerged.
In Old English the basic primary adverbs were the following ones: 
þa (then) 
þonne (then) 
þæ'r (there) 
þider (thither) 
nú (now) 
hér (here) 
hider (hither) 
heonan (hence) 
sóna (soon) 
oft (often) 
eft (again) 
swá (so) 
hwílum (sometimes).
Secondary adverbs originated from the instrumental singular of the neuter adjectives of strong declension. They all add the suffix -e: wide (widely), déope (deeply), fæste (fast), hearde (hard). Another major sugroup of them used the suffixes -líc, -líce from more complexed adjectives: bealdlíce (boldly), freondlíce (in a friendly way).
Adverbs, as well as adjectives, had their degrees of comparison:
wíde - wídor - wídost (widely - more widely - most widely) 
long - leng (long - longer) 
feorr (far) - fierr 
sófte (softly) - séft 
éaþe (easily) - íeþ 
wel (well) - betre - best 
yfele (badly) - wiers, wyrs - wierst 
micele (much) - máre - mæ'st 
The Old English Verb.
Old English system had strong and weak verbs: the ones which used the ancient Germanic type of conjugation (the Ablaut), and the ones which just added endings to their past and participle forms. Strong verbs make the clear majority. According to the traditional division, which is taken form Gothic and is accepted by modern linguistics, all strong verbs are distinguished between seven classes, each having its peculiarities in conjugation and in the stem structure. It is easy to define which verb is which class, so you will not swear trying to identify the type of conjugation of this or that verb (unlike the situation with the substantives).
Here is the table which is composed for you to see the root vowels of all strong verb classes. Except the VII class, they all have exact stem vowels for all four main forms:
Now let us see what Old English strong verbs of all those seven classes looked like and what were their main four forms. I should mention that besides the vowel changes in the stem, verbal forms also changed stem consonants very often. The rule of such changes is not mentioned practically in any books on the Old English language, though there is some. See for yourselves this little chart where the samples of strong verb classes are given with their four forms:
Infinitive, Past singular, Past plural, Participle II (or Past Participle) 
 Class I 
wrítan (to write), wrát, writon, writen 
snípan (to cut), snáþ, snidon, sniden 
 Other examples: belífan (stay), clífan (cling), ygrípan (clutch), bítan (bite), slítan (slit), besmítan (dirty), gewítan (go), blícan (glitter), sícan (sigh), stígan (mount), scínan (shine), árísan (arise), líþan (go).
 Class II 
béodan (to offer), béad, budon, boden 
céosan (to choose), céas, curon, coren 
 Other examples: créopan (creep), cléofan (cleave), fléotan (fleet), géotan (pour), gréotan (weep), néotan (enjoy), scéotan (shoot), léogan (lie), bréowan (brew), dréosan (fall), fréosan (freeze), forléosan (lose).
 Class III 
 III a) a nasal consonant 
drincan (to drink), dranc, druncon, druncen 
 Other: swindan (vanish), onginnan (begin), sinnan (reflect), winnan (work), gelimpan (happen), swimman (swim). 
 III b) l + a consonant 
helpan (to help), healp, hulpon, holpen 
 Other: delfan (delve), swelgan (swallow), sweltan (die), bellan (bark), melcan (milk). 
 III c) r, h + a consonant 
steorfan (to die), stearf, sturfon, storfen 
weorþan (to become), wearþ, wurdon, worden 
feohtan (to fight), feaht, fuhton, fohten 
 More: ceorfan (carve), hweorfan (turn), weorpan (throw), beorgan (conceal), beorcan (bark).
 Class IV 
stelan (to steal), stæ'l, stæ'lon, stolen 
beran (to bear), bæ'r, bæ'ron, boren 
 More: cwelan (die), helan (conceal), teran (tear), brecan (break).
 Class V 
tredan (to tread), træ'd, træ'don, treden 
cweþan (to say), cwæ'þ, cwæ'don, cweden 
 More: metan (measure), swefan (sleep), wefan (weave), sprecan (to speak), wrecan (persecute), lesan (gather), etan (eat), wesan (be).
 Class VI 
faran (to go), fór, fóron, faren 
 More: galan (sing), grafan (dig), hladan (lade), wadan (walk), dragan (drag), gnagan (gnaw), bacan (bake), scacan (shake), wascan (wash).
 Class VII 
hátan (to call), hét, héton, háten 
feallan (to fall), feoll, feollon, feallen 
cnéawan (to know), cnéow, cnéowon, cnáwen 
 More: blondan (blend), ondræ'dan (fear), lácan (jump), scadan (divide), fealdan (fold), healdan (hold), sponnan (span), béatan (beat), blówan (flourish), hlówan (low), spówan (flourish), máwan (mow), sáwan (sow), ráwan (turn).
So the rule from the table above is observed carefully. The VII class was made especially for those verbs which did not fit into any of the six classes. In fact the verbs of the VII class are irregular and cannot be explained by a certain exact rule, though they are quite numerous in the language.
Examining verbs of Old English comparing to those of Modern English it is easy to catch the point of transformation. Not only the ending -an in the infinitive has dropped, but the stems were subject to many changes some of which are not hard to find. For example, the long í in the stem gives i with an open syllable in the modern language (wrítan > write, scínan > shine). The same can be said about a, which nowadays is a in open syllables pronounced [æ] (hladan > lade). The initial combination sc turns to sh; the open e was transformed into ea practically everywhere (sprecan > speak, tredan > tread, etc.). Such laws of transformation which you can gather into a small table help to recreate the Old word from a Modern English one in case you do not have a dictionary in hand, and therefore are important for reconstruction of the languages.
Weak verbs in Old English (today's English regular verbs) were conjugated in a simpler way than the strong ones, and did not use the ablaut interchanges of the vowel stems. Weak verbs are divided into three classes which had only slight differences though. They did have the three forms - the infinitive, the past tense, the participle II. Here is the table.
 Class I 
 Regular verbs 
 Inf. Past PP 
déman (to judge), démde, démed 
híeran (to hear), híerde, híered 
nerian (to save), nerede, nered 
styrian (to stir), styrede, styred 
fremman (to commit), fremede, fremed 
cnyssan (to push), cnysede, cnysed
 When the suffix is preceded by a voiceless consonant the ending changes a little bit: 
cépan (to keep), cépte, cépt / céped 
grétan (to greet), grétte, grét / gréted
 If the verb stem ends in consonant plus d or t: 
sendan (to send), sende, send / sended 
restan (to rest), reste, rest / rested
 Irregular 
sellan (to give), sealde, seald 
tellan (to tell), tealde, teald 
cwellan (to kill), cwealde, cweald 
tæ'can (to teach), táhte, táht 
ræ'can (to reach), ráhte, ráht 
bycgan (to buy), bohte, boht 
sécan (to seek), sóhte, sóht 
wyrcan (to work), worhte, worht 
þencan (to think), þóhte, þóht 
bringan (to bring), bróhte, bróht
Other examples of the I class weak verbs just for your interest: berian (beat), derian (harm), erian (plough), ferian (go), herian (praise), gremman (be angry), wennan (accustom), clynnan (sound), dynnan (resound), hlynnan (roar), hrissan (tremble), sceþþan (harm), wecgean (move), féran (go), læ'ran (teach), dræfan (drive), fýsan (hurry), drýgean (dry), híepan (heap), métan (to meet), wýscean (wish), byldan (build), wendan (turn), efstan (hurry). All these are regular.