Dan K , Jan 20, 2008; 12:24 p.m.
I use B+W MRC UV's for my 77mm lenses.
I have a 50 1.8 too and I have a Hoya SHMC on it. I don't think the 50mm needs a filter though as the front element is not as exposed.
You can feel the difference in quality between the B+W, Hoya, and Nikon's.
I guess Heliopan is just as good but I've never used one myself.
Keep in mind that the MRC coating on the B+W is semi water proof and a whole lot easier to clean than the Hoya SHMC coating which smears like crazy.
B+W also uses brass mounts.
I would get a 77mm polarizer. Why would you want a polarizer for the Sigma? It's too wide, you'll get weird results. I have a B+W 77mm Multi Coated Polarizer. I hear the Nikon polarizer is actually really good.