I've used Photoshop on and off until around version 7. But I ended up using the Gimp (
http://www.gimp.org) for my CP design/layout/artwork/etc. The main reasons: It's free, I didn't own a copy of Photoshop (never did.. used it for work/school), and it's as functional as Photohop. (at least for what I was using it for)
If the OP isn't already used to using Photoshop, then it might worth giving the GIMP a shot. Both programs have similar learning curves. For those who may consider switching from the GIMP to Photoshop, there's definately an acclimatizaion period, but it's not too bad.
I'm not saying the GIMP is a Photoshop Killer(TM), but it's extrodinarily functional and easily up to the task of Control Panel Artwork duty.
For anyone that's interested, here's my CP*:

*Disclaimer: My skills at using Photoshop and the GIMP are about equal. My CP should not be used as a point of comparison between the two programs.
