Summary: There are two schools of thought on filters. One camp would say that filters are needed as protection for more expensive optics. The other camp says that the degradation in image quality is not worth the advantages. I'm clearly of the former school of thought and have filters on all my lenses.
Pros: Build quality, scratch resistance, ease of cleaning
Summary: B+W's high quality brass ring minimizes binding, allowing the filter to screw on/off a lens smoothly. The retaining rings, seamlessly bonded to the glass, secure the glass in place with absolutely no play. The matte black finish is flawless.
Summary: I use this filter mainly for my Canon EF 17-40mm f/4.0 L lens. It is thin enough to avoid any vignetting on my 1.6 crop 30D. The brass ring makes the filter feel heavy and solid. What I love most is its multiple resistant coating. I don't see any "ghost" reflection when taking landscaping photos.
Pros: High quality class, perfect multiple resistant coating
Summary: I use this filter solely to protect the front element on my Canon 24-70mm F/2.8L lens. Its a $80 protection for a $1100 lens. In that sense its reasonable, but for a coated piece of glass, it is a bit pricey.
Pros: Nearly transparent, no noticable loss of image quality
Summary: This B + W 77 mm UV Haze 010 Multi Resistant Coating Glass Filter is build like tank, made from brass so it will not easy get bend because of temperature changes plus since they build it strong the glass stay the same the way they make it (straigt) so minimize glare.
Summary: I have two of these: one for my 24-70L and one for my 70-200IS. While the filters aren't exactly cheap, I consider them insurance while out in the field. They complement the L lenses to provide weatherproof capabilities. The filter is very clear and produces no optical distortion that I can tell.
Pros: Quality: no optical distortion such as glare or vignetting.
Summary: B+W is one of the most famous companies that makes the best filters for cameras. This 77mm filter is not like any other cheap filters on the market now. It is very high quality and will not degrade your photo.
Summary: Bought a canon 17-40L/4 lens, need a 77mm UV lens. Received it yesterday, the lens is very clear, you can't feel where the glass at. Multi-cover is very good to prevent reflection. Good making, made in Germany. B+W is a famouse filter company. I give it five stars for its quality.
Summary: I purchased this UV filter for my Canon EF 17-40 4.0L lens. When I first received this filter, my felling was "why did they send a metal loop to me, there is no glass in the middle!". Then I realized that the class was so clean that I couldn't see it without holding it under the light.
Pros: Good quality, multi-resistance coated (MRC) to protect your lenses, easy to clean.
Cons: Too expensive, in comparison with other brand products.
Summary: Bought this MRC UV filter for a $1700 Canon L lens. It is expensive, but in relation to the lens it is cheap insurance. Can't see any imperfections when held up to the sun: crystal clear just like my lens. Be sure to get the MRC version.
Pros: Quality of filter glass is as good as, if not better than, the lens itself