Helios 44m-4 58mm f/2

While the Zenits might not be anything to write home about, the lenses attached to these budget soviet SLRs are definitely very well known, and for good reason.
Compared to the more popular Helios 44-2 58mm f/2 (known for its swirly bokeh) this one has much more controlled bokeh with less swirling. But even without the appeal of that, this lens is surprisingly capable. It would definitely benefit from some modern multi-coating, but it delivers a very lovely, vintage look with nice sharpness.