I love Budapest... Someone might need to chime in and correct me though, as it’s been a couple of years, and it’s quite a fluid nightlife scene...
If you’re there only briefly, it can appear a bit disjointed, and decent places sometimes seem elusive or hidden down dark alleys. It’s dead safe though in general... I always ended up staying in and around the 7th district, near Blaha Lujza tér. There’s a few alright places round here to warm up in... A rooftop place on top of the Corvin Supermarket, and both “Alcatraz” and “Old Man's Music Pub” nearby. I wouldn’t spend all night around here though, unless it’s a quieter week night or something.
The “Ruin Bars” are really cool. They’re also around this area. Definitely Google this though, as it’s all probably moved and changed name since my visit.
If you’re only here a short time, and want something easy to find, head to Petofi bridge, where you’ve got “A38 Boat”, “Zold Pardon”, and “Rio” this area should be pretty crowded, especially in warmer months. It’s going to be quite mainstream and possibly a bit touristy, but it’s a safe bet if you don’t want to search for more underground places. Don’t head here too early though.
If you’re in the middle of town still, anywhere around the “Opera” area gets quite busy. Andrassy ut, Bajcsi Zsilinski ut, and Terez. There’s a few good spots in this part of town.
Avoid Vaci in the evening... It’s full of tourists, rip off joints and stag parties.
I’ve heard good things about Hajogyari Island... I’ve only been up this way for Sziget Festival, so can’t really comment. Possibly more expensive than in town though? It's not really the sort of place you'd be staying near, so you'll need a taxi on the way home...unless you've partied really late, in which case it'll be well connected to the suburban metro thingy.
Margaret Island has a few places in the summer months too... and it's closer to the downtown...
Here’s a good sheet I found with Hajogyari in it:
http://www.rooshvforum.network/thread-5937.h...t=budapest
Budapest is quite an outdoorsy place when the weather’s good, but like a lot of European capitals, it can be quite dead here in the height of summer, apart from around Sziget, the Formula 1 where it'll be absolutely rammed (and the pubs and clubs will be dead!)
You should be able to Google most of the stuff you need, and they do a free magazine with lots of nightlife listings... When I first started going, I found the "Timeout" guide had the coolest listings and was the most helpful...