Placehold.it
This is really cool… www.placehold.it is a site that generates filler images for you. Just link to it in your css or image tags, set the size of the image and you’re good to go:
<img src="http://placehold.it/350x150">
The above image tag will give you:
You can also add color and text:
Here is a simple layout built in codepen.io that makes user of placehold.it: