I'm currently working on a list of the best sports games of all time, for all systems. I haven't yet put them in order, but here are some of the games that should definitely be considered:
Atari 2600
Baseball
Football
Basketball
Nintendo Entertainment System
Tecmo Bowl
Bases Loaded
Double Dribble
Blades of Steel
Baseball Stars
Ten Yard Fight
Track and Field
TurboGrafx 16
World Class Baseball
Power Golf
TV Sports Football
Power Leage Baseball 3 (Import)
Genesis
John Madden 93
NHL 94
Tony LaRussa 95
Fifa
Super Nintendo
NBA Live 98
Super Tennis
NCAA Basketball
3DO
Fifa International Soccer
Slam N Jam 95
John Madden Football
Sega Saturn
Fifa 96
WorldWide Soccer 97
World Series Baseball II
John Madden 98
NHL PowerPlay 96
Decathlete
Sony Playstation
NBA Gameday
Triple Play 97
Fifa 96
International Track and Field
Madden 97
Nintendo 64
Nothing I can remember
Sega Dreamcast
NFL2K
NBA 2k
NFL2K1
NBA2K1
These are just some games that I can remember off the top of my head. I need to go do some research and remind myself all the good ones.