Update: This is no longer needed as music, apps, and other content that you have purchased is always available to you in iTunes 11 on the Mac that you are signed into.
Apple will sometimes make a one time exception to re-download lost music due to a crashed hard drive or a lost computer.
Go to the “Express Lane” button located to the right of the page (listed below) and tell them about your problem via on-line chat.
http://www.apple.com/support/itunes/store/lostmusic/
We also perform iPod data recovery on iPods that have a hard drive. If you have an iPod that is sick and you need the data MacMedics might be able to help you. Don’t forget that iPods are a terrible place to store data. If your iPod gets lost, stolen, or dropped, you could lose all of your data. If your iTunes data gets damaged and you need to “download” the music off of your iPod in order to restore your iTunes library, there are ways to perform that as well.