Well besides the main first party titles (OoT 3D, AC:NL, Mario Kart 7, Fire Emblem, Pokemons), there is a new Phoenix Wright game (download only) which was is fantastic, Bravely Default which will be out soon and getting rave reviews, and is sort of a successor to Final Fantasy, Theatrhythm Final Fantasy which I played the shit out of - and I hate rhythm games, Kingdom Hearts 3D, Metal Gear Solid 3 3D and the list goes on and on.
If you getting a 3DS, I'd have to recommend an XL if you have even slightly large hands. For whatever reason the 3ds normal gives me cramps really quick in games when I never got any with the ds lite, although I'm sure you could try out both before buying.