My current 3 smaller hard drive back-ups are FULL.
I may buy two of these: one for video, one for laptop Time Machine back-up.
500 GB external hard disk with rugged, shock resistant case
Triple interface including FireWire 800, FireWire 400, and USB 2.0 for speed and universal connectivity
Backed by a 3-year warranty
Product Dimensions: 1 x 5.6 x 3.5 inches ; 8.8 ounces
LaCie 301371 500GB Rugged All-Terrain FireWire 800/ FireWire 400/USB 2.0 Portable Hard Drive – Amazon
US$155. Double this capacity would be better, but this model does not have it yet.
Leave a comment if you can recommend an alternative.
Rick McCharles 
Have you looked into a Drobo? Since I have hard 4 hard drive failures in the last 2 years (2 of them, instant failures, rather than a something with a little bit of warning). I normally keep things backed up on several hard drives, just in case, and it was lucky that I did.
My primary “redundant” drive is now a Drobo. My dad also got one. It isn’t blindingly quick, but it is “upgrade-able” on the fly, and provides redundancy (all data survives a single drive failure). Basically, you can plug up to 4 (preferably different-sized, different branded) SATA hard drives into it. Different-sized and branded because they tend to have different failure modes. Different-sized, because when you need more capacity, you just pull out the smallest driver and put a bigger one in. All this can be done while the drive is online and in-use.
Pretty happy with it so far. Note that in my paranoia, I still keep another backup of important stuff. Just because my data is stored on a redundant drive, doesn’t mean that some stupid used (e.g. me) won’t accidentally delete something important.
Take a look at http://www.drobo.com.
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