A Circular polarizer is definitely Numero Uno. Cokin (and possibly other mfgrs) now make a Warm Polarizer, which is like an 81B+Polarizer. Having both in one minimizes the added risk of lens flare when using multiple filters. Diffusions filters are great for people shots, and flowers too. I also like a 6-pointed star filter to add a little "Sparkle" to highlights. As far as B&W filters, my fave is a yellow-green (#11), at least for people portraits. It heightens contrast without looking unnatural.