Istanbul's a pretty cool city. I spent about a little over a month there and I never ran out of stuff to do or see. The city oozes with history and the energy's contagious all along Istiklal and Taksim.
For someplace cheap and nice, I would recommend the Balkans (Bosnia and Croatia) or Western Ukraine and Poland. Lviv is a pretty chillax city, and probably my favorite on the planet outside of NYC.
If you wanna' party, you can't go wrong with Berlin or Ibiza. I haven't been to Ibiza yet, but I kind of know what to expect since I go to raves that feature the same deejays spinning at Ibiza. I've done a few warehouse raves in Berlin, and I definitely recommend the city as a raving destination.
My advice, unless if you're loaded, skip the typical western European and east Asian destinations. Instead, head towards central/eastern Europe, southeast Asia, or South America.
I was in Bosnia, Sarajevo. I imagine it's better now then when I was there in the mid 90's. Bad memories!