It depends what the content was. If it was music or videos you're pretty much stuffed, as marc said above. If however it was an app, you can download them again as often as you want without paying again (Unless the app creator has released a new version and not allowed a free upgrade for owners of the previous version).
I would however add that is you lost music or videos that you have recently purchased (ie in the last day or two at most) send apple an e-mail asking them to allow you to re-download the items in question. I did this a couple of years ago after I lost a couple of tracks when my HDD died within a few minutes of downloading, and they did allow me to download the tracks again. They might do the same for you or they might not, but it's worth a try before you fork out for them again.
But in future remeber to backup, backup and then backup again.