[avgp]

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

[navs]

There's also

http://placedog.com/ http://baconmockup.com/

[user-id]

http://lorempixel.com/ is what I use.

[Michiel]

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

[poissonpie]

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

[kingkool68]

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

http://www.russellheimlich.com/blog/list-of-dummy-image-gene...