IMHO, it's a choice between the Nikon 105 and Tamron 90.
I've had the 90 forever. Thom Hogan rates it as optically equal to if not better than the nikon. But the nikon has better build quality, vr, hunts a bit less and has a little more reach which is helpful with our tanks... but it will cost you around $400 more. I think the Tamron is the best value in a macro for Nikon cameras. Although i'd like the 105, the 90 is so good I haven't been able to justify the cost of the switch.