Bargain lenses that are surprisingly good:
Chinon 50/1.9. Mine is the PK version.
Chinon 50/1.4. Again, PK mount. As good as my Pentax 1.7s, but a 1.4. However, mine had sticky aperture blades. I got mine with a Chinon CE4s, a sleeper camera if ever there was such a thing, all for £10.
Helios 50/2.0. This was an old 39mm mount version with 8 aperture blades. Awkward to use, but worth the £2 it cost me.
Pentax M 35/70 F2.8/3.5. I was pleasantly surprised by this lens, for a zoom, although the edges can be iffy. It is 2.8 nearly all the way through.
Special mention:
Not a sleeper, or particularly a recommendation, but if someone wants a dabble with super wide angle on 35mm, the budget choices are limited and prices have been forced up. This lenses failings are well documented, and allowance has to be made for above average distortion and definition fall off at the edges. Being manual focus, it is of little interest to digital users, so prices are low. If it is left at 18mm/F8, it can render surprisingly good images. The lens - the Samyang 18-28 F4.0/4.5 (you can stop laughing now). Tape the focus at the hyperfocal point, the zoom ring to 18mm and keep it set to F8, then go and have some wide angle fun!
http://www.lensporn.net/2011/12/review-samyang-18-28mm-f4-45.html