Vienna and Bratislava, both near to each other and linked by frequent trains (about 35 mins IRC) and coaches. Mind you when I went I flew KLM changing at Amsterdam which can be a bit of a clart on, but the crap flights allowed me to dash off into Amsterdam City Centre in both directions
Bratislava has popped up a few times can you get flights from the N.E to there ?
I didn't really like Bratislava, there isn't very much to do and the locals can be quite hostile. Not that many bars around either but it is still pretty cheap.