Some games that impressed me:
EB2XEEKV - Strawberry Storm Striker by yunomi. Touchscreen based arena shmup. Supports the Ciclepad Pro and likely works much better because of it. Great graphics!
N3A5E3L3 - Arcanum Stone by hiraiyukio. A great fighting game with a lot of detail to animations, characters & stages. My favorite so far!
JD2EE2QV - Solid Gunner by SmileBoom. Very well polished vertical shmup released officially by SmileBoom.
QK4N3PZF - Spooky Maze by calc84maniac. A raycasted 3D maze with spooky skeletons. Technically impressive and the library it comes with opens the door for others to make 3D games as well.
A few places to check:
PetitModem, useful for backing up and modifying over your Windows PC:
http://rei.to/petitmodem_en.html
SmileBASIC Source, an English board for posting your apps/games (en):
http://www.smilebasicsource.com/search?category=Programs
This speadsheet contains a bunch of Japanese games/apps:
https://docs.google.com/spreadsheets/d/1ihBdTe0w3GRSE-NgzqTo7i0XtMvLKqWTZ6xuVmsHiJ4/edit#gid=0
This page contains a Japanese board containing many entries: http://wiki.hosiken.jp/petc3gou/?Toukou
Also be sure to check out the Miiverse pages for both international and Japanese:
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