I bought a flashdrive with a write protect switch for the same reason. I currently have a 2gb version from pqi. They have 4gb ones as well but didnt have them in stock at the time i ordered mine.
As a side note, there are some worms that can still infect your flash drive even with the write protect switch set. I found this out the hard way with brontok and/or the rjump worm. Nasty lil buggers, took me 2 months to fully clean them out of my work place.
