(no post) = not funny, but not horrible enough to comment on
l = humorous, but don't be too proud of it... this is actually more of an insult than a compliment.
lol = hehe... kind of funny, but i'm not actually laughing out loud.
LOL!!! = i actually laughed to myself. pretty good there, chum.
oh, my god. i'm laughing so hard that i'm trying to cover it up. god i'm so embarrassed that the people i work with think i'm crazy = cheers to you! you are the funny!