(^_^) or (^-^) smiley
(`_^) or (^_~) wink
(>_<) angry, frustrated
(^o^) singing, or laughing maniacally
\(^o^)/ very excited (raising hands)
(-_-) or (~_~) or (=_=) annoyance, resignation, or sleeping (eyes shut), grumpy
(-_-;) or (^_^') or (^_^);; nervousness, or sweatdrop (embarrassed; semicolon can be repeated)
(-_-#) or (-_-В¤) vein (used to show frustration)
(В¬_В¬) eyeing something or someone, sometimes used as an expression of rolling one's eyes
(<_<) skepticism, looking around suspiciously
(;_;) or (T_T) crying
(@_@) dazed
(o_O) confused surprise
(0_<) flinch, nervous wink
(O_O) shocked
(._.) intimidated, sad, ashamed
($_$) money eyes; thinking about money
(x_x) or (+_+) dead or knocked out; giving up, lost, confused
(n_n) pleased
(u_u) annoyance, sarcasm, sometimes disappointment
(9_9) eye rolling
(e_e) mischief, distrust
(*_*) star-struck
(",) smirk
("o) s ide shocked
(-.-)zzZ sleeping
(o)_(o) alternative for tired; sometimes used to illustrate crazed
;o; or ;O; crying loudly/shouting
T_T or TT_TT or Y_Y exaggerated crying, so that the eyes are closed and tears stream down the face
I_I "What?", mellow

Complex examples

=^_^= blushing, or a cat face (mischievous)
-^_^- blushing
^n_n^ catgirl or boy
d-_-b listening to music, labeling title afterwards
~~~~>_<~~~~ weeping horribly
<(^_^)>,(>^_^)>, etc. dancing, especially used to specifically show Kirby dancing
(>^_^)> <(^_^<) hugging
(>^(>O_o)> sexual intercourse, normally used to depict rape and/or anal sex (extensible)le)
( ~^_^)~ dancing
(9ГІ_Гі)-o fighting, throwing a punch
w-('u')-w Kilroy was here (extensible)
p(^o^)q good luck
(b~_^)b thumbs-up
(p-_-)p thumbs-down
t (-_-t) or ,,l,(>.<),l,, flipping off
(^^ .)\\// giving the V-sign
m <(~_~)> m kitten
~~(=_=)~~ breakdance
\m/>_<\m/ rockin' out
\0-0/ wearing glasses (nerd)
x_x whatever