I definitely recommend Krakow, Poland. Very good club scene, cheap and lots to do and see. It's getting more touristy, so go while it's still cheap! A really nice hostel there is the Garden House Hostel. You can book it through Travelpunk's
hostel booker. It's cheap and in a great location.
Zakopane ("zahk-o-pahny"), Poland has a beautiful mountain range that's fabulous for hiking. It's becoming more of a shopping/touristy city as well, but apparently the Artist's Cemetary is not to be missed. Artists have designed their old headstones.
Slovakia - even cheaper than Poland I heard.
Of course Prague is a huge party city. The Czech Republic is really beautiful, so if you get the chance to take the train outside of the big cities and maybe site see in some smaller areas, I'd recommend it. Still cheap.