Any of the old Vivitar lenses that have a serial number that starts with "22" (Kino Optical, a.k.a. Kiron) or "28" (Komine) have been keepers in my book. I've got a handful of them and there's not a dog in the bunch.

If you can find one, the 90mm f/2.5 Vivitar Series 1 macro (actually a lens that gets you to 1:2 and a 2x matched teleconverter to get all the way to 1:1) is one of the sharpest lenses I've ever used and one of the sharpest lenses ever tested by various magazines and individuals. The 90mm f/2.8 Vivitar macro (all the way to 1:1 without a teleconverter, but heavier than the f/2.5 lens) is also bitingly sharp (I've used three examples and all three were incredible lenses). If 90mm is in the range of focal lengths you're interested in, I can highly recommend either of these lenses from my own personal experience.

The other big advantage to the f/2.8 lens is that it tends to be cheaper than the f/2.5 lens...the f/2.5 lens has a cult following and the f/2.8 lens tends to be ignored because it wasn't a "Series 1" lens.