One of my favourites: Cable. Cable is a two room nightclub with an extra room under the name of Relay, specially for live performances. It opened its doors in 2009 and won the 'Best Club in Time Out's Best of 2011 Awards'.
The entire club holds up to a thousand and each room has an own bar and seating area. There is a large covered smoking area and even a VIP area.
Cable is specialised in underground beats and bass music. Not only the music is underground, so is the venue. Literally. Cable is located in one the tunnels under the arches of the railway lines by London Bridge. This unique location is what created Cable's distinctively raw atmosphere. Big metallic airducts and bricks give this place industrial characteristics.
The sound and light and audiovisual installations are amazing. This means that if you have sensitive ears - bring your earplugs. I can tell you now that your ears will be ringing the next day if not days. But of course, it's all worth it.
For about £10-15 you can spend a good 8 hours going crazy on house, techno, dub, grime, drum and bass, and anything likewise. Drinks are relatively cheap. Or well, at least they are not ridiculously expensive.