In the 105mm range, why not try out the 105mm f/4 AIS micro. It has excellent performance, as noted above great working distance and is not a very large investment. The AIS version has a nice locking knob for the focus collar. I like the way it "paints" the background.
#1
D5100 with 105 mm f/4 micro AIS @ f.7.1, 1/1250, ISO 400 (lens is chipped).
#2
D5100 with 105 mm f/4 micro AIS @ f/8, 1/60, ISO 100
With PN-11 that came along with it (actually my reason for getting this lens, one could say I got the lens by "accident"):
#3
NIKON D7100 with 105mm f/4 micro AIS +PN11 @ f/8, 25s, ISO 100, UV-induced visual fluorescence (UVIVF).