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There's a similar service for that - but with cats! http://placekitten.com/

There's also

Let's not forget http://placesheen.com if you need placeholders of Charlie Sheen.

As a little self-promotion, there's also http://www.placeguitar.com

edit....just to link the source code in case anyone is interested https://github.com/poissonpie/Place-Guitar

There are a ton of them out there. Here is a list of them ordered by when the domain name was registered.