I had a FireFly 20GB external HDD that was small and light, but died unexpectedly. Fortunately, it wasn't a crisis.

I have a 40GB IBM exernal HDD I bought 5-6 years ago, and the thing is bulletproof. Right now it's on about its 90th foreign trip and has worked flawlessly. I keep it encrypted as it has al my stuff backed up. Downside -- needs two USB cables and isn't as small as others.

Also use a couple 8GB Transcend flash drives. Convenient, but write time is slow when putting 5-6GB on them.

Cheers,
Leo