I suggest Persona 4, because it will be awesome and I'm obsessing over it right now. It's a PS2 RPG coming out on December 9th, so it should be pretty easy to find. (It's a non-Square Enix JRPG, so it probably won't sell out.) It is rated M though, so I'm not sure if your Mom is okay with that or not. It's only M because some of the personas are partially nude or have sexual designs, and because it has drunk high schoolers once.
If that doesn't fly you could always get KH Re: Chain of Memories or something. (PS2 Dec. 2)
And if you want a DS game: Get 'The World Ends With You' if you don't have it yet.