Don't think you'll be ready to go home after the awesomeness that's Dark Knight? I know I won't be - meet up with other fans for after parties. These venues and events will still be open:

Thursday morning (for those going to midnight showings)
Shadow Lounge in SoHo: http://www.spoonfed.co.uk/event/shakeit_1925_20080723_2200 - until 3am
DeeSFactory at The Factory: http://www.spoonfed.co.uk/event/deesfactory_1058_20080724_0200 - from 2am

Thursday night/ Friday morning (for people going Thursday after work)
Thursday Throwdown at 19:20 - http://www.spoonfed.co.uk/event/thursdaythrowdown_1318_20080724_1800 from 6pm
Beats Working at Fluid - http://www.spoonfed.co.uk/event/beatsworking_1474_20080724_2000 from 8pm
It's a Thursday Thing at Zoo Bar - http://www.spoonfed.co.uk/event/it39sathursdaything_1208_20080724_2200 from 10pm
Club 3D at the Factory - http://www.spoonfed.co.uk/event/club3d_1058_20080725_0200 from 2am