(^_^)       The basic smiley face (egao).
            Note that it is made with a straight line for the mouth
            because there are no keybord characters that curve up

(;_;)       A crying face (naki).
            The semicolons represent eyes with teardrops coming out of them

(^_^;)      Nervousness (hiyaase).
            The semicolon represents beads of sweat.

(*^_^*)     Blushing and happy (niko!).
            The asterisks represent blush marks.

(^_^;>)     Embarrassment (hazukashii).
            This one is a little difficult to understand,
            but the 'greater than' sign represents your bent arm as you
            scratch your head, something that Japanese people often do
            when they are self-conscious.

(^_^)b      Thumbs up.

m(_)m       I'm sorry/Thank you (gomen nasai/arigatou).
            This symbol depicts a person doing a seated bow.
            The "m's" are hands and the brackets and underscores are
            the top of the head rather than a face.

(-_-)zz...  I'm tired (nemui).

(*_*)       Surprise or shock (maitta).

(>_<)       Pain/failure (itami or shippai).
            The "greater than/less than" signs represent your eyes
            shut tight as you grimace in agony.

(^_^)V      Peace/Good news (niko).

(^O^)       Happiness (ureshii).

(^_^)/~     Bye Bye (bai bai).
            The slash and tilde represent your arm waving a handkerchief.

(^_-)       Wink (uinku).

(^3^)       Kiss (chu).

p(^^)q      Good luck/Go for it (bambatte).
            The "p" and "q" represent your clenched fists held in
            front of you.

See more at

http://staff.aist.go.jp/k.harigaya/doc/kao_lis.html