There are a lot of options. I personally use a Sigma 105mm EX f/2.8 and I'm quite happy with it. Sometimes I use the 1.4 Teleconverter which makes it a 147mm f/4.0, good for when you need just a bit more reach.
I've also used some unconventional ways to shoot small things...
This one shot with a Sigma 120-400mm. This shot not heavily cropped, but close to the nearest point it would focus.
And this done with a Sigma 70-200mm with a Kenko extension tube which someone else mentioned.
As you can see, I also have a hard time figuring out which is the best option.