riding spirits was a cool game for the playstation, it will be a little hard to find new as it came out when the ps2 first came out (2002).
It tired to be the Gran Turismo of motorcycle games, offering tons of bikes and tracks. Alot of diehards though game play was a little weak Still it was cool to see bikes you never see in motorcycle games like the 1972 kawasaki h2, triumph bonneville, honda cbx, honda cb400 supersport, etc...It was also cool that you could build these bikes into wikked track bikes/cafe racers with clip ons, upside downs, modern mags, and such. Too bad you can't race them on open streets (oooohhhh, now there is a game idea, do we have any programmers in the house?).
Ducati world was also a neat ps2 game (also pc). You can race only ducatis whihc I didn't mid so much since it let me pretend for a Breif second what it would have been to be Mike Hailwood. The riding physics were really good in it except two things 1) you couldn't hold a wheelie past 40 mph (the comp automatically drops you down), and 2) occasionally you would either low side or high side for no reason what so ever. Lots of hidden bikes though and some really neat obscure duc iron. Plus you could slightly mod them.
To me the best motorcycle games will always be the road rage series of the 1990s. Urban street brawling meets urban street riding, plus you had to dodge cars and chains. The bikes were kinda limited but I am a PC gamer at heart.
As for the system the new x-box is coming out so I think they will stop making games for it soon. Playstation won't be releasing another system until late 2006 and ps2s are cheap right now. The graphics and playability are much better on the xbox however. Personally I sold my xbox to my brother when he went to college, I'd rather spin wrenches.