I went to Belgrade after Exit festival the other week and really enjoyed it. I have to say my opinion may have been somewhat swayed by the fact that the girls were HOT though!

(ahem, excuse my shallowness but a man's got to take these things into account). Seemed really lively too with a buzzing atmosphere and a lot of alfresco dining late on a monday night.
Spent several days in Budapest before and after Exit and fell in love with this place too. I'd love to know - what's the electronic music scene like? And how much is rent?
Barcelona - been to Sonar three years in a row so visited a fair few times. LOVE the architecture and the atmosphere.
Berlin - Seems to be the capital of all things electronic these days. Never visited but heard great things.
If anyone could give me an estimate of living costs in any of these places it would actually be appreciated very much
