Got a song stuck in your head? Get a quick fix with Songerize, a super simple Google-esque search engine for popular audio tracks. Just type in the song name and artist, and within seconds it'll start playing right under the results. It's powered by SeeqPod, which offers a more robust feature set, but without as much simplicity. Songerize doesn't tell you where the tracks are from or where to get them, but in testing it managed to pick up nearly every mainstream artist and popular hit I stuck in.
Another service that has been doing this with a little more finesse (and a business plan) is Songza, which we took a look at back in November. It'll tell you where to buy the music, and where they got it from--which can be pretty helpful if you're trying to make it a part of your permanent collection.