:-) Your basic smilie. This smilie is used to inflect a sarcastic or joking statement since we can't hear voice inflection over the web.
;-) Winky smilie. User just made a flirtatious and/or sarcastic remark. More of a "don't hit me for what I just said" smilie.
:-( Frowning smilie. User did not like that last statement or is upset or depressed about something.
:-I Indifferent smilie. Better than a Frowning smilie but not quite as good as a happy smilie
:-> User just made a really biting sarcastic remark. Worse than a :-).
>:-> User just made a really devilish remark.
>;-> Winky and devil combined. A very lewd remark was just made.

Those are the basic smilies. Now here are some somewhat less common ones:

(-: User is left handed
%-) User has been staring at a green screen for 15 hours straight
:*) User is drunk
[:] User is a robot
8-) User is wearing sunglasses
B:-) Sunglasses on head
::-) User wears normal glasses
B-) User wears horn-rimmed glasses
8:-) User is a little girl
:-)-8 User is a BIG girl
:-{) User has a mustache
:-{} User wears lipstick
{:-) User wears a toupee
}:-( Toupee in an updraft
:-7 User just made a wry statement
:-[ User is a Vampire
:-E Bucktoothed vampire
:-F Bucktoothed vampire with one tooth missing
:-* User just ate something sour
:-)~ User drools
:-~) User has a cold
:'-( User is crying
:'-) User is so happy, s/he is crying
:-@ User is screaming
:-# User wears braces
:^) User has a broken nose
:v) User has a broken nose, but it's the other way
:-& User is tongue tied
=:-) User is a hosehead
- - -:-) User is a punk rocker
- - -:-( (real punk rockers don't smile)
:=) User has two noses
+-:-) User is the Pope or holds some other religious office
`:-) User shaved one of his eyebrows off this morning
,:-) Same thing...other side
|-I User is asleep
|-O User is yawning/snoring
:-Q User is a smoker
:-? User smokes a pipe
O :-) User is an angel (at heart, at least)
:-P Nyahhhh!
:-S User just made an incoherent statement
:-D User is laughing (at you!)
:-X User's lips are sealed
:-C User is reaally bummed
:-/ User is skeptical
C=:-) User is a chef
@= User is pro-nuclear war
:-o Uh oh!
(8-o It's Mr. Bill!
*:o) And Bozo the Clown!
3:] Pet smilie
3:[ Mean Pet smilie
E-:-) User is a Ham radio operator
:-9 User is licking his/her lips
%-6 User is brain dead
[:-) User is wearing a walkman
(:I User is an egghead
@:-) User is wearing a turban
:-0 No Yelling!
:-: Mutant Smilie
|.-) User only has one eye
,-) Ditto...but he's winking
X-( User just died
8 :-) User is a wizard
C=}>;*{)) Mega-Smilie -- a drunk, devilish chef with a toupee in an updraft, a mustache, and a double chin

Note: A lot of these can be typed without noses to make midget smilies.

:) Midget smilie
:] Gleep...a friendly midget smilie who will gladly be your friend