Wired has a review up of solid state drives, which would be what I would get if I was in the market for an external harddrive.
PS- if you don't have an external drive, you should really get one. Imagine how upset you would be if all your work, data, papers, photos, and music disappeared when your computer bit the dust.
Cloud storage is good, but should not be your only backup.
Read the Wired reviews here
The ones they look at are:
$99 LaCie Porsche 1TB SSD
2 year warranty, aluminum case
THIS IS THE ONE I WOULD BUY
I've had nothing but good experiences with my LaCie products and I like the look of this one (I am just the kind of fool for marketing gimmicks that they love).
$258 Verbatim Store n Go 3.0 SSD 256GB
2 year warranty, plastic case
$303 IoSafe Rugged Portable SSD 1TB
3 year warranty, heavy, sturdy
$140 OWC Mercury On the Go Pro 1TB
1 year warranty, formatted for Macs