Someone already said it on this thread, but I must reiterate that Project Justice is a must buy if you like fighting games.
For RPGs, there's the obligatory SoA, but you might as well buy the enhanced version to support RPGs on the GC. Grandia II is also available, which is good, but I wouldn't consider it as good as Grandia I. The dungeons just got tedious after a point, and the story just wasn't as good in my opinion. Aside from the big two, there's the Evolutions, but again, they made it to the GC. I guess you could also buy the Sega Smash Pack to get Shining Force and Phantasy Star II.