Plymouth nightlife is quality. You have the big places: Oceana, K2, C103, Walkabout, Revs, all of which are great and do student nights throughout the week, although as said, if you dont go out on one of their student nights then it can be a bit rough, especially on Union street.
At the weekends, or before/after a night out, the area around the student village is pretty buzzing with smaller places like Roundabout, Cuba, bang Bang, Fresher and Proffesor, Skiving Scholar, Ryde and others. The SU is also decent at the weekends.
Most nights here are also relatively cheap, with most drinks seemingly about £1.50. Best nightlife I've experienced in a city, probably not as good as bigger cities like London Bristol Manchester Brum ect, but its still very good, and probably cheaper.
Only thing I'd say is watch out for trouble.