The polarizing filter is one of the best filters for eliminating glare from surfaces (inlcuding water). For those who don't yet own one, I would like to add a couple of suggestions to Mr. Schade's recommendations:

1) When using the polarizing filter, consider using a tripod. With most polarizing filters, depending on the brand, you lose between 1 to 2 stops of light. This can mean slower shutter speeds and more chance of user induced shake and blur.

2) If you have a camera with autofocusing, you'll need a CIRCULAR polarizing filter. If you have a manual focusing camera, you can use a LINEAR polarizing filter.

3) The filters only work from about mid-morning to late afternoon. If the sun is below a certain angle relative to the horizon, the filter becomes another piece of dark glass.

4) These filters are great for outdoor travel shots...really increases the blues of the sky and the contrasting whiteness of any clouds.

5) If you expect quality results, don't scrimp on any piece of glass that goes in front of your expensive lens...expect to spend at least $40+ for an average filter (the better ones will cost even more). IMHO, some of the better brands that I've had good luck with include Nikon, Canon, B&W & Heliopan...