White, pastel, or black backgrounds are safest. Tiled backgrounds shouldn't have visible seams. The following list links to samples of sidebars, textures, and patterns I've created, some using objects and photos I've scanned:
Sidebars
Blend
Shadow
Torn
Pines
Flower
Lace
Burlap
Canvas
Mud
Cement
Grain
Stucco
Fiber
Twirl
Dabs
Cube
Cat
Rosebed