Quote Originally Posted by Canuck935
Well with digital cameras basically the only filter effect that can't be duplicated in software is the polarizing filter. Some of the polarizer filter effects can be duplicated, but not when used to cut reflections/glare. Oh and buy good filters. I've seen some bizzare things happens with cheaper filters.
Also, if you are using a DSLR, you must buy a circular polarizer, not a linear.

Other filters, for the future if you need them, various NDs and maybe an ND grad (although I prefer layering in PhotoShop).