I pretty much use the same filters as everybody else. I use a pola, a #25 red, and a medium yellow. I'd like to get a yellow green and an orange, but it's no hurry. I standardized on 82mm filters and have step rings for all of my lens sizes.

Another helpful thing I've learned to do is put the stop correction right on the filter. I print tiny labels with a p-touch label printer and stick it to the edge of the filter ring. The more I do things like that the less I have to interrupt my creative thinking with technical thinking while I'm working.