Decorating the back of a car? Bumper stickers?

How can I decorate the back of my car without damaging the paint? Are there special types of bumper stickers or other alternatives that I can put on my back windshield or the backdashboard?

Just pondering on how I can spruce up my car on a low budget.

Other decals sites

• Permatex 9103-6PK Windshield Repair Kit – Pack of 6 | Honda CRV Parts
• iOwnTheWorld.com » Blog Archive » Annoying Leftist Bumper Stickers
• Michael Bay to produce low-budget alien film » GordonandtheWhale.com