I recently was pleasantly surprised to learn that Linux Game Publishing (http://www.linuxgamepublishing.com/) are working on PPC ports for some of their games. Majesty already ships with a PPC binary (even the demo), and according to one of their developers, there should be ports of Ballistics, Soul Ride and possibly Disciples 2.
I hope they won't regret this. :) -- Earthling Michel Dänzer \ Debian (powerpc), XFree86 and DRI developer Software libre enthusiast \ http://svcs.affero.net/rm.php?r=daenzer