If money is an issue, the 50mm f/1.8 is an excellent lens and can be had for about $100. Very sharp, great walk around lens. The other suggestions are good though. If you can swing it, the Tamron 90mm Macro, Nikkor 60mm Micro, and Sigma 150mm Macro are all great lenses but will set you back $300-400.
For macro, I personally suggest a tripod and shutter release. Of course with some practice you can certainly do it free handed.
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