The first free on-demand music service I ever encountered was Songerize. The page was a simple white box on a red background. Enter the name of a song, and it would scour the Seeqpod database of user-posted content, find the song, and begin streaming it immediately.
There were no fancy playlist features like Grooveshark, no social-networking features like Imeem, no embedded player or song locker like LaLa, just instant gratification. Unfortunately, Seeqpod declared bankruptcy and around the same time, Songerize became useless.