See my sig for my recommendation.
Granted, I share a Seagate 500GB external with my sister, but my uncle put it in an enclosure for us. I've heard that WD drives hold up better in general, but that's hearsay.
It gets pretty darned hot during a full backup, as Night Hawk alluded to.....but that is partially because of USB 2.0 speeds backing up my Caviar Black 640GB internal drive. The OS partition doesn't take long enough for it to really get hot, but the data partition does.
I'm hoping to score a new external drive at tax time, that can utilize my tower's front esata port, then I will give this Seagate up to my sister. So hopefully Uncle Sam is feeling generous this year!