Accommodation in the UK: This is a web site that allows you to contact accommodation in the UK direct, and to make offers on rooms available, and for the hostel to contact you back.
Backpackers UK: Guide to the UK's budget accommodation.
Globetrotter Inns - Cheap independent hostel accommodation in London and Edinburgh for backpackers: Accommodation for the independent backpacking traveller on a budget. Hostels in London and Edinburgh offer inexpensive self catering backpackers accommodation with multi occupancy and private rooms.
Hostel Finder UK and Worldwide: Hostels UK and Worldwide. Online Booking & Confirmed Reservations.
Hostels in Northern Ireland: An up to date site listing hostels (both YHA and independent) in Northern Ireland, including prices, addresses and web links.
Youth Hostels Association (YHA): Hostels in England and Wales with a useful hostel search function and booking facilities.