I purchased the B+W 82mm MRC UV Filter to protect and complete the weather sealing of my new-at-the-time Canon EF 16-35mm f/2.8 L II USM Lens - Canon's first EF lens with 82mm filter threads. Unfortunately, I felt the physical vignetting caused by this normal-thickness filter + lens combination at 16mm was too great when using a full frame body. I prefer a B+W 82mm Slim MRC UV Filter for this lens. There are downsides to slim filters - primarily price and the slip-on (slip-off would be a more appropriate term) lens cap it requires.
You need to decide for yourself if the slim version is worth the trade-off to you. Use the mouse-over feature at this link to view the vignetting caused by this combination ...
Of course, there are other 82mm lenses. On a longer lens (or possibly other wide angle lenses), the B+W 82mm MRC UV Filter is probably the best 82mm UV filter available.
Do not buy a cheap UV filter. Read the B+W 77mm MRC UV Filter Review for more information. The B+W 82mm MRC UV Filter is essentially the same filter with a different thread size.