Because the scratch-resistent part of my iPhone scratched I decided to get some protection, may or may not work, but I figured it wouldn't hurt.
I ordered a shield for the front over at Zagg and thanks to a bit of looking around I got a nice discount (and they now offer a 30% discount till 2008-12-31) and free shipping. For more discount codes check out Chris Pirillo's site. I also have two codes for a 20% discount valid until 2009-01-25, so if you want one drop me a note.
I have not yet tried these shields, but I hear they work really well. They sell them for all kinds of phones and cameras and laptops.