Minolta MD Tele Rokkor 135mm f/3.5
I picked this up on eBay ridiculously cheap for £19.97 (I was the only bidder) in November 2014. It also came with a Micro Four Thirds adaptor (which the seller had over tightened so it was jammed on) but I got it off with the vice and sold it on eBay for about £4 so the nett cost was about £16. Extraordinary!
As you can see from this photo of David it works well as a portrait lens coming in at about 200mm equivalent.