You basicly have two choice as I can see it... Gamecube doesn't have enough RPGs to make mention of, the only GOOD one (IMO) being Skies of Arcadia. And you can pick up a dreamcast and the original for probably about the same amount the game itself would cost.
Playstation has a large amount of console RPGs... The FF games, for example... But most of them are just that; Console RPGs.
X-Box has less RPGs, but then again, it has less games overall so far. It has a few real gems though: Morrowind, and Knights of the Old Republic, for example, are two insanely good RPGs. Morrowind: Game of the Year edition was just released with some content from the expansion packs for the PC included. It also has some great roleplaying games comming out... Jade Throne, Fable, etc.
It's got some other games that may or may not appeal to you as well... Shenmue II, for example. And it's got a ton of more simplistic games, some of them even using RPG settings... Dungeons and Dragons: Heros, Baldur's Gate: Dark Alliance, Hunter: The Reconing, etc.
There are some other points to consider with the two systems, as well...
Playstation does have some MMORPG games... Basicly, ok, it has Everquest. If that interests you, that's something to consider. It's not bad.
In terms of online play, X-Box is generaly the clear winner, though... With its unified X-Box Live service, it's really hard to compete with it.
If by any chance you are interested in playing DVDs with it (I doubt it, few people are anymore), X-Box wins out... It needs an extra attachment, but you wont have problems with DVDs playing in it, like the PS2 sometimes does.
One nice feature is you don't need memory cards with the X-Box... so none of those to keep track of, and buy new ones constantly. On the other hand, its harder to take a saved game to a friends house or something. You can buy memory cards for the x-box, but it kinda negates the whole purpose of the internal hard drive.
In terms of system hardware, the Playstation 2 is nearing the end of it's life... It's not bad, per say, and with a good developer, it can still really shine. But it's quantifiably not as good as the X-Box or even 'cube in that regard.