Rick mentioned LondonTown.com in his England guidebook. Any other good ones you can reccomend.
For accommodations? I used a number to search, always checking with TripAdvisor.com; visitlondon.com, smoothhound.co.uk, findlondonhotel.com/londonoffers, and many have mentioned finding bookings on priceline.
I used hostels for the first time on my trip last month and they were wonderful. We always had private rooms. Just do your research - I looked for ones that scored low on the 'fun' scale. www.hostelworld.com
Booking.com has always been reliable with tons of reviews and good prices for us.