"A quick and simple image placeholder service. Just put your image size after our URL and you'll get a placeholder."

"Spritemapper is an application that merges multiple images into one and generates CSS positioning for the corresponding slices."

"Dragonfly is a Rack framework for on-the-fly image handling in Ruby. It is suitable for using with web frameworks such as Rails(2.3 and 3), Sinatra, etc."

Nicely done, space-themed tag browser for Flickr images.