This site includes various free self-guided walking tours of London, passing many tourist attractions, and a cheap London sightseeing tour by bus. Also ideas for cheap self-guided ...
http://www.londonforfree.net/

Visitors worry that London is an expensive city but there really is so much to do for free from museums and galleries to free music and walking tours.
http://golondon.about.com/od/thingstodoinlondon/tp/free_Lond ...

Information, directions and maps for various free sightseeing walking tours around central London, passing many of London's major tourist attractions.
http://www.londonforfree.net/walks/index.shtml

You will regularly hear from travelers how expensive London can be, but London has lots of places that are free including museums and galleries, musical and ceremonial performances ...
http://golondon.about.com/od/londonforfree/London_for_Free.h ...

Our guide to 10 brilliant things to do in the capital that don't cost a penny ... London for free Our guide to 10 brilliant things to do in the capital that don't cost a penny
http://www.guardian.co.uk/travel/2008/jun/11/london.free

We've now closed down. We'd like to say a big "Thank you" to the very many people who have helped us over the years since we started in 2000.
http://www.londonfreelist.com/home.asp

From free attractions to good value eats, find out how to get the most out of London ... You don't have to spend a fortune to have a great time in London. If you're on a budget ...
http://www.visitlondon.com/people/budget/

Discounts on leading London hotel and bed and breakfast accommodation. Sightseeing, attractions and other tourist information. Theatre tickets, dinner and theatre packages and more
http://www.londontown.com/London/Eccentric_City

Enjoy up to two FREE hotel nights in London when you fly round trip to London or stop in London on your way to any of our worldwide destinations.
http://www.britishairways.com/maylondonforfree

Find loads of free stuff in London. Don't just throw away your old belongings, find them a good home here.
http://www.gumtree.com/for_sale/freebies/