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.
Now, Songerize creator Will Johnson is back with a second take on the same concept: Songite. The interface looks almost identical to its predecessor, and the concept's the same: instant gratification.
There are two important differences between Songite and Johnson's last work, however. First, you can now arrange songs into playlists, then share those playlists via simple URLs. Second, Songite now draws content from YouTube and Imeem, two sites that have more or less received the blessing of the big record labels and are in no danger of being sued out of existence. Bookmark it for the next time you've got a song stuck in your head and simply have to hear it right now.