WebSnapr is a free online service that lets you take snapshots of other websites.
Here is an example of one of my sites:
Using WebSnapr if very easy. Just use the following URL to generate a thumbnail:
http://images.websnapr.com/?url=[url]&size=[size]
Of course, just replace [url] and [size] to make the magic happen. You can get up to 5 different sizes by setting the [size] parameter. These are your choices:
* T = 92x70 (example)
* S = 202x152 (example)
* M = 400x300 (example)
* L = 640x480 (example)
It might take a few seconds before the thumbnail is captured. If so, you'll see a "Snapshot currently in queue" message. This will be gone as soon as your thumbnail is generated.