Currently Being ModeratedApr 30, 2012 4:16 AM (in response to jxdavies)
It depends on where you live. You should be able to download virtually everything again for free if you live in the U.S except for some movies, audiobooks and extra iTunes content with movies.
This explains how you can download again for free. You must be using the same Apple ID that you bought the content with as well.
This explains what is available where you live.