I recently found out (from a separate site, crackberry.com) about a company called Zagg who produce a protective film called the Invisible Shield for phones, mp3 players, etc. It's apparently a derivative of stuff that protects rotor blades from damage in US military helicopters.
I bought one for my Blackberry Storm and it arrived today. It 'seems' to be a good product but as I only received it, I won't be able to tell for sure for a while yet. Still, if it stops my keys scratching the screen or cover, I reckon it's $25 well spent. It took a while for delivery, mind...nearly 2 weeks.