My favorites are the ones made by PocketPCTechs.com, but I'm wouldn't say they're really cheap. They do last a really long time though, which in the end saves money.
-------------------- Lisa Gade Editor in Chief, MobileTechReview
Search Google or eBay, buy something bigger and then trim it down to the size you need! Else, if you are picky about using branded stuff, Google navprotector ? they use some really long lasting material that doesn?t make bubbles when you stick it on