If you're looking for a bargain check out betterbidding.com. Thanks to the tips there I stayed at the Hilton Islington in October for $85 through Priceline, and it was fantastic. About 1 block from the Angel tube station (Northern Line, Zone 1, easy access to everything with a connection or two). There are tons of pubs and dining options in walking distance, and a Sainsbury grocery store, too. The area was REALLY nice, no worries after dark whatsoever.

I also stayed at the Crowne Plaze Shoreditch on the same trip which is a great hotel but not as nice a neighborhood for dining/shopping and much farther from the tube (although there is a bus stop out front to take you there).

Either way, I saved over 50% off the going rate, and -$100 per night for a 4* in London is way better than booking direct.