I like this plan to finance the purchase of a new ship for Greenpeace.
Pick an item, and buy it for them, rather than just selecting the random donation level that most charities ask for. Once an item is bought, it appears in the catalogue as Sold Out. It's a bit like a wedding list in that there are lots of small pieces (cutlery, pens), and also some bigger pieces. So far most of the small pieces have gone, but very few of the big pieces, which might be a problem with this approach.
(Horrible, horrible site though - why can't I turn off the music, for example?)
In a similar vein, The Girl Store for The Mahindra Foundation asks you to fund schooling for girls in Africa, with pictures of the children who are being funded, and the items they need. Once the money has been raised the girl is labelled 'Off To School'
Both of these approaches show that it's often more of an incentive to give if you can see the change you create in a practical way.