here's the hostel where i stayed last week: http://www.hostelworld.com/availability.php/AceHotelKensington-London-10044 it's brilliant, clean, safe, breakfast included. also really close to hammersmith, but unfortunately a bed in the 8-bed-dorm is 15 pounds a night now instead of the 10 i paid. would still be ok with me, but the cheap room is not available anymore for the 27th and 28th. *sigh!* but for those who leave on the 27th or don't mind paying a bit more, it's a great place. guess you should book soon though, it's quite popular.
there's another one that has really good ratings, and long (the canadian guy who was queuing with us at the hammersmith) also said it's very good, he's been staying there, it's this one: http://www.hostelworld.com/availability.php/PalmersLodge-London-14348 guess it's not so close to any of the venues though.
and i'm currently thinking of staying at this one in february: http://www.hostelworld.com/availability.php/MEININGERCityHostelHotelLondon-London-17414 - i've been staying at the meininger in berlin, which was very good, and a friend of mine was at this one in london and she also said it's good. also has good hostelworld ratings.
actually, those 3 are the 3 top rated ones on hostelworld.