KROKODIL
There used to be a restaurant called Krokodyl in the Old Town however it was a bit quiet and is long closed now.
Thinking of the Old Town, there are a couple of clubs there and some good studenty ones on Krakowskie Przedmieście leading up to it.
Plus there's Bar Warszawa on Krakowskie Przedmieście which is big and lively at weekends (or was, when I was last in there).
We go to Loreta on ul. Widok nowadays which is a 30+ crowd, expensive and chic. Nice music too, but a place to dress up for.