Belgrade is cool. Novi Sad too. We went for exit festival which was cool.
This was my route around the Balkans.
Belgrade - Novi Sad - Sarajevo - Mostar - Split - Dubrovnik - Kotor - Podgorica.
Stopped at quite a few places in-between too but I can't remember names right now (Plitvice Lakes and The waterfalls in Croatia I can remember) I think the Balkans are some of my favourite places to travel in the world. I love it. Podgorica was a hole though, worst place out of the lot. Kotor probably my favourite.