Games include: Syndicate, the Ultima and Wing Commander franchises, The Witcher 2 (all out for the first time on Mac today), Machinarium, FTL, Syndicate, Sim City 2000, Dungeon Keeper, Tiny and Big: Grandpa's Leftovers and Crusader: No Remorse. Right now GOG has 50 games available for Mac, 28 of which are only on GOG.
Good Old Games is expanding to include not only Mac games, but PC games for Mac.