[ubernoob]

In no particular order :
Mutant League Football/Hockey (counting the franchise as one game here.)

World Series Baseball (the game that made me never forget Jeff Blauser of all people. I was a monster with him.)

Joe Montana Sports Talk Football. Just a blast of a game. I still have both that game and my Sega Nomad.

Honorable Mention:
The basketball playoff matchup games as mentioned here.
Tecmo Super Bowl series (even the PSX versions were fun to me.)
Both Front Page Sports football and baseball franchises.