I spent a day and a night in Belgrade on the way back from Syria on the train. The weather wasn't too great as the city was covered in fog, but that didn't stop me. The fog did cause one embarrassing moment with the Serbian Parliament building, I walked right past it in the morning and didn't spot it in the fog, it wasn't until the afternoon (when the fog had risen a bit) did I spot it on the way back to the Hotel.
Belgrade seems to be a nice little city to wander around in, and it's very compact, so you can do it all on foot - I'd like to revisit when the weather's a bit better. There are parts that seem rather 'soviet' especially the buildings near the Hotel Moscow, but that kinda adds to the city's appeal, that and the network of overhead cables for the trolley buses.
The main shopping drag was all decked out with the Christmas lights, and there were plenty of shoppers out doing their stuff. At the end of the main street there is the Kalemegdan Fortress. From there you can get great views over Belgrade and the Sava and Danube Rivers - but all I could see was fog. Oh well, you always need a reason to come back to a place!