There are several good and recommended vendors of screen protectors for the BlackBerry. These have been mentioned over and over in the threads at BlackBerryForums.com
Vintage BECO Impedance Bridge Model 250-C
Zareba EAC200M-Z 200-Mile AC-Powered Low-Impedance Electric Fence Charger
Heathkit Impedence Bridge 1B-2A
Parmak DF-SP-LI Solar Pak 6 Low Impedance 6-Volt Battery-Operated 25-Mile-Ran...
Agilent E4991A RF Impedance/Material Analyzer