I came across this service a while ago but I thought that it was worth sharing. When you're developing a website, sometimes you need to use placeholder images because your client may not have all of assets ready. This website serves up placeholder images of kittens!! You simply use the URL of their website followed by the height and width that you need. Such a fantastic idea. I mean, come on? Who doesn't love kitties??
<img href="http://www.placekitten.com/200/300" width="200" height="300" />