Had a quick search but I'm still unsure of which filter to choose. Both filters are the same price but I don't really know which is the better of the two or what one type offers that the other dosen't etc..
Hoya 77mm Digital Multi-Coated (DMC) Pro1 UV Filter
Hoya 77mm Super HMC Pro 1 UV (O) Filter
It would basically be for protection for use on a Canon 10-22mm EF-S on a 20D.
EDIT: Done a few more searches & got a few threads on the same subject.