The unofficial smilie dictionary
Your basic smilie. This smilie is used to inflect a sarcastic or joking statement since we can't hear voice inflection over Unix.
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.
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 ones...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
User is wearing sunglasses
Sunglasses on head
User wears normal glasses
User wears horn-rimmed glasses
User has a mustache
User wears lipstick
User wears a toupee
Toupee in an updraft
User is a Vampire
Bucktoothed vampire
Bucktoothed vampire with one tooth missing
User just made a wry statement
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
User has a broken nose, but it's the other way
User's nose is sliding off of his face
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
User is asleep
User is yawning/snoring
User is a smoker
User smokes a pipe
Megaton Man On Patrol! (or else, user is a scuba diver)
O :-)
User is an angel (at heart, at least)
User just made an incoherent statement
User is laughing (at you!)
User's lips are sealed
User is really bummed
User is a chef
User is pro-nuclear war
It's Mr. Bill!
And Bozo the Clown!
Pet smilie
Mean Pet smilie
Your pet beaver is wearing goggles and a hard hat.
User is a Ham radio operator
User is licking his/her lips
User is braindead
User is wearing a walkman
User is an egghead
User is wearing a turban
No Yelling! (Quiet Lab)
Mutant Smilie
The invisible smilie
User only has one eye
Ditto...but he's winking
User just died
8 :-)
User is a wizard
Mega-Smilie... A drunk, devilish chef with a toupee in an updraft, a mustache, and a double chin