Not sure if many of you have tried it, but Try Giff Gaff. Its apparently truly unlimited internet withno fup. So long as its for personal use and does not include tethering. Cost 10 quid a month via a "goody bag" and includes free unlimited text and a hundred minutes of calls. (15 quid its the same but 300 minutes if calls). I tried it and its getting good data speeds, its still in beta, but now its set up I'm very pleased. Few teething problems on set up but good customer services. Uses o2 network.
giffgagff.com
giffgagff.com