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Numbers
0 零 / 〇* zero/rei
1 一 ichi
2 二 ni
3 三 san
4 四 yon
5 五 go
6 六 roku
7 七 nana
8 八 hachi
9 九 kyū
10 十 jū
20 二十 ni-jū
30 三十 san-jū
100 百 hyaku
1,000 千 sen
10,000 万 man
100,000,000 億 oku
1,000,000,000,000 兆 chō

other:
1 - ichi
2 - ni
3 - san
4 - shi / yo
5 - go
6 - roku
7 - shichi / nana
8 - hachi
9 - kyuu
10 - jyuu
11 - jyuu ichi
12 - jyuu ni
13 - jyuu san
and so on...
20 - ni jyuu
21 ni jyuu ichi
22 - ni jyuu ni
23 - ni jyuu san
and so on...
30 - san jyuu
40 - yon jyuu
50 - go jyuu
60 - roku jyuu
70 - nana jyuu
80 - hachi jyuu
90 - kyuu jyuu

100 - hyaku
200 - ni hyaku
300 - san Byaku *note - is byaku, nt hyaku ~^ ^~)
400 - yo hyaku
500 - go hyaku
600 - RO Pyaku *note - its pronounce as 'ro' ending with a 'k sound but no 'u' ; also it's pyaku, not hyaku - correct me if im wrong, i cant really remember this one ><)
700 - nana hyaku
800 - shichi hyaku
900 - kyuu hyaku

1000 - sen
2000 - ni sen
3000 - san Zen *note - is zen not sen)
4000 - yo sen
5000 - go sen
6000 - RO sen
7000 - nana sen
8000 - hachi sen
9000 - kyuu sen

10,000 - man

100,000 - hyaku man

Shi is associated with death, so if you're counting people and you say shi, it's kind of like cursing them. So instead you would say yon. The same applies to the number seven, shichi/nana.

Actually for 1-10 there are two ways to say all of them. One is the chinese way and the other is the Japanese way. when Japan started to break away from China (I think in the Heian period) The Japanese tried to make their own number system. some of them are used more than others but they all have their practical uses!

Chinese way
1 いち (ichi)
2 に (ni)
3 さん (san)
4 し (shi)
5 ご (go)
6 ろく (roku)
7 しち (shichi)
8 はち (hachi)
9 きゅう (kyuu)
10 じゅう (juu)

Japanese way
1 ひと (hito)
2 ふた (futa)
3 み (mi)
4 よ/よん (yo/yon)
5 いつ (itsu)
6 むい (mui)
7 なな (nana)
8 や (ya)
9 ここの (kokono)
10 とお (too)


As as a side note 800 is はっぴゃく (happyaku). *^_^*