FTP or Free to Play.
 
After playing FFXI, WoW and all the other P2P (Pay to Play) games I've actually started playing Free games while in School so I don't get too addicted. They’re bit kiddy but most of them aren’t too deep so I don't get so addicted my school starts to suffer.
 
I tried:
 
Gunbound
Maple Story
Cabal Online (which is pretty addictive and broke my own rules)
Rumble Fighter (Also too addictive)
Grand Chase
and Latale
 
Latale is pretty good for school because I just end up hanging out in game doing for the most part nothing and just chatting with people. At first when my friend got me into it I thought it was a retarded kiddy game but after awhile it got pretty good.