I've been looking for something similar, I have the old version Nikon 60mm macro and even on DX it just isn't long enough. The lens that currently has my fancy is the Sigma 150mm Macro, it's supposed to be absolutely superb. The Nikon 200mm is optically very good but it's big and heavy and can be a bit of a pain to use (from what I've read). If you plan to tripod mount it, you can't go wrong!