Now listed on the HFL Delicious pages: British Cartoon Archive
The British Cartoon Archive holds the artwork for more than 150,000 British editorial, socio-political, and pocket cartoons, supported by large collections of comic strips, newspaper cuttings, books and magazines. The collection of artwork dates back to 1904 and includes work by W.K. Hasleden, Will Dyson, Strube, David Low,Vicky, Emmwood, Michael Cummings, Ralph Steadman, Mel Calman, Nicholas Garland, Chris Riddell, Carl Giles, Martin Rowson, and Steve Bell, amongst many others.
BCA is freely available at http://www.cartoons.ac.uk/.