I would recommend a Marumi filter; they are relatively cheap, but good. They're the OEM manufacturer for a few other quality brands. The problem is that they're hard to find, though I see you can now get them through Amazon.

As Guffa notes, you'll want a circular polarizing filter (abbreviated CPL) as linear polarizers are incompatible with most autofocus systems.

Other good brands include B&W and Hoya.

Be sure to get a multi-coated filter, to cut down on reflections. For the Marumis, this is the DHG or Super DHG lines. Polarizers aren't a good item to be cheap on; the cheap polarizers are really quite awful.

Your lenses should be marked with the proper filter size (on Nikon lenses it looks like "72ø"), and that info will also be in the manual.

I would recommend a Marumi filter; they are relatively cheap, but good. They're the OEM manufacturer for a few other quality brands. The problem is that they're hard to find, though I see you can now get them through Amazon.

As Guffa notes, you'll want a circular polarizing filter (abbreviated CPL) as linear polarizers are incompatible with most autofocus systems.

Other good brands include B&W and Hoya.

Be sure to get a multi-coated filter, to cut down on reflections. For the Marumis, this is the DHG or Super DHG lines. Polarizers aren't a good item to be cheap on; the cheap polarizers are really quite awful.

Your lenses should be marked with the proper filter size (on Nikon lenses it looks like "72ø"); if not, check the lens cap. That info will also be in the manual.