Cambelt is a full-featured service for placeholder images. It works by using special URLs as the image source (like
http://cambelt.co/468x60
will generate an image with the mentioned dimensions) and has support for custom text + images with custom colors.
The service is even possible to use custom fonts, font sizes and ask for a specific filetype (like
http://cambelt.co/400x300/Custom+Text?font_size=12&format=jpg
).
Also, besides the standard placeholder images, it can provide icons in any size as well.
