Well, I personally know loooots of developers who want to put other site’s thumbnails on their site. One of my friends wrote an article on his blog a long ago and I gave the link away to the developers. But that never helped because that is based on some 3rd party API, which is not free after a couple of snaps.
Today again a developer asked me for similar solution and I found Websnaper 2.0 They are capturing screenshots for free and present them at your chosen size. This is really a nice service and very useful for those who needs it.