I know what a polarizer is used for but looking at the wide range of prices for a given size they are, obviously not all created equal.

Can someone fill in the blanks?

Filters are like most photo equipment, you get what you pay for. Get the best one you can afford. The higher end filters are designed better, and made with better materials to help reduce lens flare, and to give you a sharper image. I would also suggest you get the filter that will fit on your largest lens. (I'm refering to filter size, not lens size.) Then get a step down ring to fit your other lenses. That way one filter will cover all your lenses. Sorry I can't give you more specifics but I'm sure someone else can help you better than I can.

One thing you're paying for with better filters is that they're more color neutral. They won't affect the color, but still will do their job. I've had a Nikon filter and it was very good, and currently use a Hoya SMC which is also good.

Thanks gents.

That reinforces what I had guessed.

MJS - Great idea about the large filter and adapters, but one question: How does the adapter effect the use of a hood?

How does the adapter effect the use of a hood?
Doesn't work, usually. Typically, I don't use a hood with a polarizer so that I can turn it for the effect I want. I'll use my hand to shade the lens if necessary.

You may want to look at slim-mount filters which won't vignette with wide angle lenses. In some cases with really wide lenses the edge of the filter can show up in the corners (vignetting) and the slim mount filters take care of this problem because they're about 1/2 or 2/3 the thickness of a regular filter. They cost a little more (but you won't have to buy another one), you won't have front filter threads for putting on another filter (which would pretty much guarantee vignetting with wide lenses) and use press-on lens caps that aren't really solid, but I'm glad I went this route. I've got a 77mm and it will fit all of my lenses, using step-up or step-down rings if needed.