A couple of odds and ends:
DO NOT buy a Segate GoFlex. They have some bug that causes the hard drive to never spin down when idle.
Also, Don't buy a "For Mac" drive. The only difference is that the specifically "For Mac" packages come formatted HFS+. However, reformatting a drive is simple and quick with Disk Utility. The 30 seconds of labor is not worth the premium those drives usually command.
I generally prefer drives from the original manufacturer. It's one less hassle when dealing with warranty issues (if you have them).
Companies like Other-World Computing sell "Premium" drives, which have some additional warranty, but also command a premium cost. For example, a Western Digital 2TB external drive is $109 from Newegg, while a similar 2TB external from OWC (with the same drive, internally), is $149.
Furthermore, I tend to recommend buying external hard-drives locally (Cosco is great for this), since drive problems tend to be immediately apparent, or happen after several years. Additionally, I have had many more bad drives from ordering online (I think it is the shipping), then purchasing locally.
Also, with price-sensitive things like external hard-drives, there is no real price difference locally vs online.
If you are really concerned about recovery in the instance of a failed drive, an external enclosure with two drives in RAID-1 is probably a better bet then something like OWC's data recovery warranty. OWC sells them pre-stuffed with drives, but you can buy the drive carrier and drives separately for much less, and assemble it yourself.
This also has the advantage that drive failure does not lead to you having to ship your drive in to get the data back. In a RAID-1 system, your data is never unavailable, and you just replace the bad drive. With most systems, you don't even have to turn it off.
Is there any reason you want a bootable copy, rather then a Time-Machine backup? Time machine is nice because it also provides versioning, and restoring from a backup is pretty painless.