Last night, I added X-Scape (renamed "3D Space Tank" for Europe, but frankly it's a stupid and unfitting name, so I don't use it) back into my current rotation of games. It's the 2010 DSiWare sequel to the 1992 Japan-only 3D Game Boy game by Argonaut Software, simply named X (it contained the first ever appearance of composer Kazumi Totaka's famous little song, too), made by the ex-Argonaut folks at Q-Games (who also worked on the original two SNES Star Fox games, Star Fox Command, and 3DS remake, Star Fox 64 3D). It's superb, and plays like a Star Fox 3 could well have done, had the Star Fox 64 series not eliminated the original games from continuity and rebooted the franchise.
Others in the current rotation include Mega Man ZX Advent (DS), Mario Tennis Open (3DS), Art Academy (DSi-enhanced; Retail version), Mario Kart 7 (3DS), Skylanders: Spyro's Adventure (3DS), I Must Run! (DSiWare), VVVVVV (3DSWare), and Kirby's Dream Land 2 (GB; 3DS Virtual Console).