Friday 15 October 2010 1.16pm
Try Homeswapper http://www.homeswapper.co.uk/
There are a lot of web sites out there that will try to fleece you for money (or pretend they are free and then ask you for money later) - most of which are run by the same organisation.
Homeswapper is run by a consortium of Councils and Housing Associations and is probably the most reasonable and reliable site out there for this sort of thing.
Good luck with your search!