Hi,
I usually do mine own work. I use GIMP, and a great old program called Paint Shop Pro, (bunch of plugs for this). As far as scaling goes my 1590B artwork comes out to 442 x 838 pixels, and my 125B artwork is 725 x 1365 pixels. I'll put up a few of my designs, and if you want I could rough out some ideas for you...just give me a "theme"...space, abstract, horror, etc.
Also, VERY IMPORTANT! I made the mistake of trying to put decals over dark paint. Unless you're using a laserjet it's a bad idea!! I couldn't make out anything, and had to scrape the decal. I'll put up a few of my pedal artwork, and you can get back with me if you want me to through some ideas your way...