NOTE, Nov. 2010: After some major changes to its service, eMusic no longer allows free re-downloads of purchased songs. Redownloads are still possible, but they now require additional payment.
One of the key differences between eMusic and other music download services that work with the iPod is that if you accidentally delete a song from your computer or iPod, but you got it from eMusic, you can redownload it without having to pay for it a second time. No other iPod-compatible download service offers this feature.
Not all the MP3s you downloaded from eMusic will always be available; songs can be redownloaded as long as eMusic and the record company who owns the song maintain their contract. If the song is removed from eMusic, it removed from your download area as well. Also, you must maintain your eMusic membership to take advantage of this feature (though if you let you membership lapse, and then rejoin, your download history, and ability to redownload, is maintained).
So, assuming that the song you want to redownload is still available on eMusic, here’s a step-by-step guide to redownloading eMusic songs.
Begin by navigating to eMusic.com and logging in to your account.