Did Vienna and Bratislava a few years ago, flew to Bratislava (loads cheaper than Vienna), taxi to Vienna (about an hour) and stayed a few nights there, took the boat along the danube (again about an hour) back to Bratislava and had a few nights there before flying back.
Riga is good too if you fancy it.
Krakow is excellent, not sure if it's still there but there was an ice cream parlour in the square when we we visited, all on offer were laced with some kind of alcohol. Zakopane mountains is a good trip out along with the obvious places.
Berlin and Barcelona are both great.