1) I'm interested in this too, lemme think of a list
Super Puzzle Fighter 2
Super Street Fighter 2X
Twinkle Star Sprites
Street Fighter Alpha 3
Yu Suzuki Game Works Vol. 1 (includes many classic games ported to Saturn)
Virtua Cop 2
Daytona USA (dc version is greatly enhanced though)
Sonic the Hedgehog 1 (on sega smashpack on DC and on sonic jam on saturn)
Real Sound, Kaze no Regret
Black Matrix (DC version contains additional content and enhancements)
Other titles of note
-All neogeo ports on saturn (a significant part of the saturn fighting library: King Of Fighters, Samurai Shodown, Fatal Fury, etc.) can unofficially be played with fullspeed emulation via neo4all, a neogeo CD emulator for dreamcast
-Certain games that were released on PSX could probably be partially emulated through bleemcast, sometimes with fairly playable results. This would probably cover a lot of third party sports games, certain fighting and racing games (Battle Arena Toshinden)
Between all of these avenues, you could maybe play 1/10 of the Saturn's library on the dreamcast anyway