Cowboy Bebop? They already made a game! It's only in Japan though.
But you can still get it on Ebay if you're lucky.
The Cowboy Bebop game is a shooter/flying. You have to fly Spike's Swordfish and shoot at targets...I think.
It looks really cool, and I was thinking about getting it, but I still have to wait until I collect some dough.
The Trigun game really looks cool. I'm going to try to find out more info, and if I do, I'll be sure to let you guys know.