Mario and Mario Kart...
I know you said not to mention them, but they really are great games (Super Mario 3D Land starts out quite easy, but it gets quite tough in the extra levels).
Otherwise...
Star Fox 64 3D is as amazingly awesome as it was on the N64.
Nano Assault is decent but a bit too short (worth it for cheap).
Samurai Warriors Chronicles is really good... but getting Dynasty Warriors Next on the Vita should be a pretty much equivalent experience so it's your call.
I've heard great things about Devil Survivor Overclocked but I have yet to check it out myself.
On the downloadable side, Pushmo is actually quite good. It starts out stupidly easy, but quickly enough the puzzles get quite good.
The best VC titles are probably Donkey Kong, Gargoyle's Quest and Link's Awakening DX.
And Kid Icarus Uprising is coming out this month, I'm pretty hyped for that.