D.I.Y. macro with 50mm 1.8
Ive used an old minolta 35-70 with a reverse adapter for a while now and get awesome results (sharper than my mates nikkor 60mm macro) without needing a tripodor to shoot straight down, having said that it was a bit of a pain with the manual exposure. Results were even better with a 2x converter.
Ive just picked up a 90mm 2.5 Tamron Macro and its stunning and much easier to use. But i'll keep my reverse setup cos it gets me even closer than1:1. Other advantage is most macro lenses double up as great portrait lenses. A sigma 50mm 2.8 would be a better option than 50mm 1.8 nikon with any kind of macro adaptor.