According to Ace's chart, the 9kb is the best bet for the PSR2100, and by extension, for the PSR3000. This is the Case that I use. http://www.kraftmusic.com/static/charts/ace0404.pdf

I like the Kace bag because of the 1) double pockets, 2) ample fit (I keep a tupperware container next to the keyboard that has a/c adapter, headset mic, and mic cable), and 3) low price.

Heads up. Keep a piece of foam in the case that covers the top of the keyboard. My PSRs used to get all scratched up and once an LCD got cracked. No more.

I prefer not to go with a case with rollers because I like a carrier that can handle my keyboard, keyboard stand, and speakers in one trip.

Good luck!

Beakybird