Oh dude, I LOVE fighting games, my favorite genre, some of my favorite franchises are actually fighting.
My top ten games are (In no particular order):
Street Fighter 2
The King of Fighters (Any from 97 - 2004)
Mortal Kombat(Any)
Super Smash Bros Mellee
The "VS" series. (Ties between Marvel Vs. Capcom, SNK Vs Capcom 2 and Tasunoko VS Capcom.)
Dragon Ball Z Budokai and Budokai Tenkaichi
Soul Caliber 1-4
Dead or Alive
Tekken (any)
Fatal Fury 2
... Yeah, the list could go on...