Well, heres a place I recomend for recent PnM charts, themes, and characters.
Colorful Canvas - for feeling pomu 2nd- Official Website
However, you have to do some tweaking with the banners at their PMS files, so they can show.
And chances that you can't unzip "Akiba Pop", "Spring Pop", and "Starry Pop". :\
And then there are the offical IIDX BMS files. If you are despearate, that is.
bms terminal v1.5 ~HAPPY SKY~
Some cute or Touhou BMS files:
kbwnk.net
You can also find some "BMS" files at BemaniStyle.
Meanwhile a home for themes based on Pop'n Music games.
::: Pop'n KH ::: - A Pop'n Music website <-- It's closed now. So live with Colorfull Canvas/Colorfull Channel skin...
Finaly, I will share my (Or ChaoFreak's) Feeling PoMu characters.
Trickster Online's Bunny Flow Flow Lotte (Carnival 1P, 10 2P) Minit's White-Merry Gir-Fangirl Nyami Timer (PnM Party ver.)
BONUS:
Sanoyara Zetsubou Sensei PMS file and Character! EDIT: Going back in time... Here are the older FP characters done by Chao Freak or other users.
Two new feeling pomu characters Chilly Character and PMS file...