Reading about The Million Dollar Homepage reminded me of an idea I've had on my files for a while: 'The great eBay piece-of-paper auction'.
What we'd do is start selling a single, sizeable blank roll of paper on eBay. Obviously initially its worth would be pretty much zero. However, we'd ask celebrities to autograph (and possibly contribute photos) to the paper. The value of the paper would increase as it attracts more autographs (and bids) and thus the project would snowball as is gets more attention and publicity.
I'm sure a sizeable sum could be raised for a charity. Maybe the succesful final bidder could cut up the paper and auction the fragments to raise even more funds?