The 105mm f/2.8 is an excellent lens for macro shots, you can't go wrong with it. Of course, remember that with focus breathing, the lens becomes slower (I believe it becomes something like f/4.9). The 105mm would be considered Nikon's flagship macro, but you could save a few bucks by going with a 3rd party lens, such as the Tamron 90mm f/2.8, or the Sigma 105mm f/2.8. They're both pretty good, but the Sigma has pretty terrible AF.
You could also look at some of the shorter focal length macro lenses from Nikon, such as the 85mm DX micro, with a slower aperture of f/3.5 but a lower price tag. There's also the 60mm f/2.8 micro, and finally the 200mm f/2.8 AF micro (but that's a bit out of your budget, they're selling for at least $1400 on evilBay).
I hope that I helped you with your decision,
Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories
"There are no rules for good photographs, there are only good photographs."
- Ansel Adams