[Y]ou can search for any artist and play their songs within seconds, for free. SeeqPod doesn't transcode the music as it streams, so you hear it in its original form as scraped from MP3 blogs, personal web pages, and anywhere else on the internet that hosts MP3s.Link
Or, you can use SeeqPod on an iPhone to browse the internet's music pretty much as you would the music on an iPod. Choose a letter, then an artist, and boom -- you see a list of songs by that artist that are playable right then and there (thus the tagline: "playable search").
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects