I have a multi tiered back up plan, maybe over the top but here is what I do:
1) Time Machine, seems obvious.
2) HDD Clone using CCC, I clone both my boot and data drives and keep it off site from my house. I update it every month.
3) PhotoBucket, I put all my photos on PhotoBucket in macro albums, 2008, 2009, etc, I used to use MM gallery, but well Apple decided no one wanted that anymore.
4) DropBox, I back up my documents and a bunch of data settings to DropBox. I also have a little program that pulls the masters out of iPhoto and the Metadata and moves them to my DropBox photo gallery. This serves two purposes, first it gives me an easy album by album replication of my iPhoto pictures and gives me another online source for back ups. In reality I do not need the PhotoBucket option, but I already paid for it for two years, so I just use it. Now what I do is synch those pictures to DropBox and keep them local, why? Well because I have the space right now, and by doing so, TM will back up my DropBox photo folder, so if my iPhoto library poops the bed AND I cannot get to DropBox I still have the master pictures...I know redundant, but HDD space is so cheap, why not. I use DropBox for other things anyway so it seemed to be a why not option.
5) I have a NAS at home that I back up my iTunes and home movies to and use for home sharing to the family iPad and iPods.
I still would like to back up my iTunes library and home movie collection to DropBox, but the size of them is cost prohibitive when compared to my drive clones so they have to do for now.