pkgbackup, xbackup, a lot of options in cydia. However, it should be noted that from my experience using pkgbackup, it only saves a somewhat "list" of your cydia apps, and then redownloads them.
Keep in mind though by redownloading them, this means if you want to stay on a certain version of a cydia app, say 1.0 for examples sake, and the most recent version is 2.0, you will only be able to download the 2.0 version.
If I'm wrong (I hope I am...) then someone please tell me, but sadly I don't think I am.