Japanese terms
 I used to use a ton of Japanese on my page, but now I'm using it less and less because I find sites that excessively scatter Japanese in with English to be kinda annoying.  And in case you're wondering, I took a semester of Japanese at college level so I do know vaguely what I'm talking about (but if you know more Japanese than I and want to correct me, that's great, do so, I'll learn something.)  The reason I put this up here at all is in case you watch unsubbed anime you'll know a tiny bit of what's going on (or if you go to excessive Japanese pages you'll know WTF the person is saying).
nihon: Japan (add -go and it's the language, add -jin and it's Japanese people)
eigo: English (this is important if you're in Japan..^_^)
ohayo: good morning
shimatta: darn it
gomen: sorry
konnichi wa: hello
minna: everyone (could also be used with a title such as minna-san)
ne: hey (or this could also be used with words like gomen ne, matta ne, ja ne, etc.)
baka: stupid
(person's name) no baka!: Idiot! (like Usagi no baka)
anata, kimi: you (kimi is formal and usually masculine, anata is informal)
anata-tachi or kimi-tachi: you (plural, but it literally means you and everyone else with you)
no: of
e: to (as in we're going to Tokyo, it'd be "Tokyo e ikimasu")
ni: same as e, or could mean the number 2
nani: what
doko: where
itsu: when
ikura: how much
henshin: transformation
senshi: soldier, as in Sailor Senshi
sugoi: cool
kakkoi: also means cool
suteki: yet another word for cool
onee: older sister (usually has a title after it like onee-chan)
onii: older brother (usually has a title after it)
hai: yes
iie: no
iya: no (to an action, like "no, don't do that")
ara: oh
sensei: teacher, but could also be used for a manga artist (Takeuchi-sensei, Fujishima-sensei...)
fuku: clothes or uniform (like sailor fuku)
kawaii: cute
Minna, henshin yo!: Transform, everyone!
urusai: shut up
demo: but
ja ne: goodbye
anou: um
otousan: father
okaasan: mother
watashi, atashi, watakushi: I (feminine, although watakushi is more polite and atashi is more informal)
boku, ore: I (masculine, though usually younger boys use boku and men (or egotistical younger boys like Satoshi (Pocket Monsters) use ore)
itai: ouch
watashi-tachi (or boku-tachi or whatever): we (literally, myself and everyone else)
doushite: why
daijobu ka: are you okay (if you leave out the ka then it means "I'm all right")
yurusenai: I will not forgive you
no da: it means "you know," but it can also be added to the end of a sentence to mean something that should be obvious (I think this is how Chichiri uses it in Fushigi Yuugi, and that's how I use it)
desu: the polite form of the be verb (such as "Watashi wa Usagi desu" means "I am Usagi")
da: informal form of desu
deshita: past tense of desu
datta: past tense of da
hayaku: hurry
nigero: run
yogata: I'm glad
yo: an emphasizer in the feminine form, like to say "daijobu desu yo" means "it's definitely all right" or something like that.
(domo) arigatou (gozaimasu or gozaimashita): thank you (the domo is optional at the beginning, and gozaimasu (or gozaimashita for past tense) is optional at the end, I think those make the statement more polite depending how much you add on it)
domo: thanks (more informal than saying the whole thing)
ganbatte (kudasai): good luck (the kudasai at the end is please (they're very polite, they say "please have good luck" *hee*)
onegai (shimasu): please (adding shimasu means please do this)
chikushou: the closest Japanese equivalent to the s-word
kisama: a very rough way to say "you", kinda like saying "you bitch" or something similar
onore: same as kisama, rough way of saying "you"
Counting in Japanese: ichi, ni, san, yon/shi (both are acceptable), go, roku, shichi/nana, hachi, kyu/ku, ju, juichi etc.  I'd go farther, but it gets complicated.

Titles and honoraries
In Japanese, people are addressed by their name and some kind of title.  What title depends on who the person is and how well the person addressing that person knows him or her.  Actually, not addressing a person with a title is an insult to that person (or a sign that you're extremely close to them, like Haruka and Michiru don't usually use honoraries). So here are the titles, basically in order of least formal to most formal.

-chan: used for a young female (usually) that one knows very well.  This can also be used as a term of endearment.  It can also be used with young males (under ten) or males that one knows very well (i.e. Usagi calls Mamoru, Mamo-chan.)
-kun: used for males, usually underclassmen.  Such as in Evangelion, everyone calles Shinji either "Ikari-kun" or "Shinji-kun"
-san: used for someone who you don't know too well, or can also mean Mr. or Mrs. or Ms. The Inners call the Outers by Haruka-san, Michiru-san, etc.  Also when you first meet someone you usually call them by their last name and then -san, such as Tsukino-san. (and this is what we use in Japanese class)
-senpai: used by lowerclassmen to upperclassmen, such as Makoto referring to her old boyfriend as her senpai.
-sensei: used for teachers, manga artists, or just people who you respect a lot and who have taught you something.  Such as, most people on the net refer to Naoko as Naoko-sensei or Takeuchi-sensei.  Or Haruna-sensei, who is Usagi's teacher.
-dono: kinda like -sama, which is a title of respect.
-sama: a title of great respect, usually used for lords or ladies or anyone who demands that much respect.  Like Diana calls Usagi as Usagi-sama because she knows that Usagi will be Neo-Queen Serenity.
-tachi: it means "this person and everyone with them" or it could be used as a plural (such as senshi-tachi).  It isn't really formal or informal or anything, unless you add another honorary after it, such as Usagi-chan-tachi.