you want a free recommendation for clear filters: I use the Hoya Pro1 Digital filters. I spend some time in brackish wetlands, and consider any degradation these apply to my files (I can't find any) a worthwhile tradeoff for keeping salt-spray and blown sand off my lenses.
I have one circular polarizing filter: the B+W 77mm Kaesemann Circular Polarizer MRC Filter. I would buy it again. I think this opinion is widely shared: