Plenty, at the moment but they are getting on the more expensive side already.
- Carl Zeiss lenses particularly the:
- 35mm Flektogon f/2.4 or f/2.8
- 35mm Distagon f/1.4
- Flektogon-licensed versions. These have the same lens design as the Carl Zeiss ones but produced in either USSR or France:
- Angeniex 35mm f/2.8 Retrofocus
- MIR-1 Automat 2.8/37 - This is the actual focal length that the Flektogon and Angenieux use.
- 35mm and 28mm Takumars, both f/3.5s - Be wary that 35mm M42s at f/2.8 or slower usually have a smaller rear element than usual, making extinction in the OVF a bit more quick vs lenses with larger ones.
- Super Takumar 35mm f/2.3 - Rather rare but decent enough. The rear element on this one is much larger than usual.
- SMC Takumar 35mm f/2.0 , both the older fat model and the newer one. Be careful with the yellowing of the thoriated glass, although it can be mitigated using a UV light.
- Helios 58mms. They are at the short tele- end but with my K-3 it's perfect for portrait. The centre sharpness can be off the charts, though, and many times, one would like a diffuser filter as the lens would show the blemishes in high resolution. Take note of an extremely high sample variation present with Helios 44 lenses. We used to be able to ask the vendors to get us the sharpest sample possible but the eBay sellers are now properly limited.
- For an 85mm, the Jupiter-9 2/85 is just something to grab right now. It makes rather beautiful portraits on small format or "full-frame"
Those are the usual popular ones. To be fair, many M42 produced up to the early 70s can be quite sharp and full of character. As long as the optics are clean, they are worth a try.