Boomer
http://left4dead.wikia.com/wiki/The_Boomer
Hunter
http://left4dead.wikia.com/wiki/The_Hunter
Commonly accepted hunter mentality: Cat or wolf like behavior, pack mentality.
Smoker
http://left4dead.wikia.com/wiki/The_Smoker
Tank
http://left4dead.wikia.com/wiki/The_Tank
Charger
http://left4dead.wikia.com/wiki/The_Charger
Jockey
http://left4dead.wikia.com/wiki/The_Jockey
Spitter
http://left4dead.wikia.com/wiki/The_Spitter
Witch
http://left4dead.wikia.com/wiki/The_Witch
CUT FROM GAME SO I EXPECT THESE TO BE RARE BUT I GUESS ILL LIST THEM:
Screamers
http://left4dead.wikia.com/wiki/The_Screamer