Gunstar Heroes, Dr. Robotnik's Mean Bean Machine, and Alien Crush confirmed so far. Update: You can add Ice Hockey for NES to that list.
Update: Nintendo has also added Ice Hockey for NES to this week's new releases.
Both Sega and Hudson have spilled the mean beans about their contributions to tomorrow's Virtual Console update. Hudson's website lists just Alien Crush so far, but Sega's Virtual Console page not only lists Gunstar Heroes and Dr. Robotnik's Mean Bean Machine as tomorrow's releases, but also details their Virtual Console schedule through the end of the year:
Space Harrier II - December 18th
Toejam and Earl - December 25th