I've not had much of a need beyond a polarizer for saturating colors, and a skylight for removing UV. The graduated ND sounds, in theory, useful. Back when I used B&W film, the deep RED, Yellow, and Green filters were useful. Now I shoot in color and use the Channel Mixer in photoshop for the same affect. I can see that some of the starburst, rainbow, etc. would be fun. But I'd have to find them in a garage sale or on eBay. ALL of the photoshop filters are fun!