When it comes to deciding which filter to get, never go pass this review:
http://www.lenstip.com/113.4-article...d_summary.html

It is a scientific analysis of common brands, from the cheap and nasty, cheap and cheerful, to the super expensive ("I have more money than sense") varieties. You will be surprised at the results.

PS. They also did a review of polarising filters, just do a search on there.