Ruckage's stuff, Neotron games (all the non-bennugd ones work), alex's games, Glouton (you have to rename "glouton" to glouton.gpe and use that to play otherwise it just runs the intro).
You could also play Jenka's Nightmare (Cavy Story mod) if you've already decimated Cavy Story itself.
Quasists stuff is pretty impressive and fun sometimes, FleshChasmer runs great, but FleshChasmer 0 requires major underclocking the Pandora and running the .gpe in the system folder.
Floaters is always fun too! Friq, although a little buggy is a sweet clone of gimme friction baby! Ladykiller is fun too, along with nanobounce and xenitris (just incase you feel like playing extremely zoomed in tetris
)
Payback FOR SURE, if you bought the download copy it works wicked! Perfect fit and most of Akuma no Hoku's puzzle games are good for killing a bit of time. Tower of Gowno is a nice little rogue-like (very similar to Powder)
Project Zero for a nice little Schmup, but you have to hold your Pandora sideways, so it's kinda awkward. Quartz 2 and Retrovirus (non-RTS one) can be fun to kill some time with.
Round 'em up is pretty sweet, although can be a PITA. ScorchedGP if you like scorched earth/worms like games!
Space Varments is ok using controls, but I'd love to get touchscreen working... Super Pixel Jumper (and other thatotherdev games)!!! Thruster and Spout too...
I find tikka dungeons to be fun for being just an alpha, same with Triple Triad X...
Warehouse panic and Wind and Water are always solid!
Chopper Challenge (do believe this is one you have to underclock otherwise it goes too fast!)
Ghostpix, Monkey game from wiz has that old Gameboy feel to it and on that note, Crocodingus crashes sometimes but is still fun and very nice looking!
Roadfighter if you need an old arcade monaco-style racer
Zombie Sorbet and ZNumbers2x can be fun too...