Based on a couple of several day trips to Budapest in 2002 and 2007.
Budapest is definitely one of the best cities in Eastern Europe (I personally liked it better than Prague). It is large and vibrant and a great combination of old and new. Scenic location, beautiful architecture, good cafés and clubs and of course the famous spas.
I will continue to explore the city on weekend trips from my current Vienna basecamp. In the meantime, here's a few useful links...
Accomodation
Boomerang Hostel (including online guide)
General Information
Sights
Bars & Clubs