=] or :) or C: - A simple smile, use it when something is a little funny, or when somethng good happens, or when you’re happy.
=[ or :( or :C - A frown, used for times when things are a little sad, or when you’re giving you the guilt trip and you want something. Example: =[ Please, can you tell me that secret?
=D or :D - A big smile, used for when great things happen, or when things are actually really funny.  Also when you’re extremely happy about something or glad for someone.
=P or :P - A happy stick your tongue out smiley.  Use it when something someone did was funny but stupid, or when you just said a joke, or called someone stupid not really meaning it.
='] or :’) - A happy smiley with a tear, basically meaning you’re so happy that your crying, like in situations when you're proud of someone, but it's sad at the same time.
='[ or :’( or :’C - A frown with a tear. Use it when something is pretty sad, but not tragic.
T__T- A smiley that's crying,  Use it when something is extremely sad or tragic.
^__^- Squee! Bliss.
^_^' A little tiny sweat drop. Also use it when someone says something stupid that they THINK is funny, but really isn't, so it's basically a polite laugh that's fake. Also used after someone says "lol" to something that wasn't even remotely funny, which shows they have nothing better to say, which proves them a loser.
^^;- An over dramatic sweat drop. Commonly used for awkward moments.  Use after someone said something embarrassing or you just said something embarrassing. Also use when said something that made you feel a little uncomfortable.
-^^- - A blushing smiley, used for any moment, where you’d, well, blush!
=X or :X- A smiley with it's mouth sealed. Use it after you just blurted out something you probably shouldn't have, or if someone says something really gross that makes you wanna vomit
;]- A winky smiley.  Use it if you say a secret or after you hear a secret, or if you’re joking about something. Also can be used when confessing something such as “You’re really cute ;]”
^_~ - A winky smiley. It's the same as ;] But only looks good with certain fonts, so I'll use either or.  
;D- Really happy winky smiley! Use as you would use ;] but only with my enthusiasm!
XD - A smiley with an extremely happy face I do suppose, use when something is REALLY funny or downright stupidly funny.
XP - A more exaggerated stick out your tongue smiley. Use it when someone says something pretty funny and extremely stupid. Also can be used when you say something you think is pretty funny.
>_<- A smiley with a squished like face, use it after something kind of dumb was said or something someone did that was kinda dumb or when something was funny but shouldn't have been. Or like one of those "ha ha what the--?" moments.
x_x - A dead smiley. Use when
x_X - the Living dead smiley. I have no idea what it means but It’s almost like a zombie… yes, let’s go with that.
=0 or :0 - A smiley with its mouth wide open. Use it when you’re nonetheless shocked, or someone says something awesome, but unexpected.
o_o - A smiley with wide eyes, use it when someone says something scary or when someone says something scary or really weird.
o_O- Same as above but with confusion mixed in.
-_- - A smiley that shows irritated-ness and frustration.
=| or :| - A smiley to use when you’re unsure about something. That or you’re just feeling a little bit down about something.
=/ or :/- Same as above... but a little less dramatic.
@_@ - A smiley used when something is confusing
!_! -A smiley to use when you realize or remember something.
~_~ - A smiley that just screams “Really now? Are you that dumb?”
={ or :{ -It’s a guy with a mustache!
=o{ or :o{- Monocle mustache man!
8]-A Cocky smiley. Use it when you said something that was self gloating, like "I'm super duper cool".
8D- Super cocky man... super.
=3 or :3-Squee! Happy!
+__+- Huh?
=__=- DOUBLE frustration/anger.
;~;- A smiley that’s crying, squiggly mouth and all. Use when something is just that sad.
._. – A smiley with TINY eyes. Yes. It can be used in many ways. When you feel really little and not the coolest being in the world, also when something dumb or awkward was said. The possibilities are endless.
>:C or >=C- A very angry frowny face smiley. Use it when you’re pretty mad about something!
>:D or >=D- A very evil genius looking  smiley. Use when you feel that way.
>:3 or >=3- Use when you’re cute, but have an evil plan.
0:) or 0=) or C:0 or C=0- a very angelic smiley. Use when you’re an angel.

*_*- Puppy dog eyes. Use when you need to bust those out on the internet.
*w*- Puppy dog eyes with a cute mouth. Who can say no to that?!
<_< or >_>- A very suspicious look; use when you’re suspicious or just said something suspicious. When used together something is up!
=# or :#- Use when saying “My lips are sealed!”
D:- A gasp-like smiley. You can use it in any scenario where you’d make a semi gasp or just an open mouth facial expression.
xD- ALMOST like XD but when things are more silly than hilarious. Or when you simply have a typo and didn’t capitalize the x.
>w<- When things are silly and cute. Not quite like its cousin, >_<.
<(^.^<) or (>^.^)>  or <(^.^)>- Let's dance, shall we?