I've heard many stories of external hard drives overheating and failing because the manufacturer failed to put a good cooling system inside the case. Can anyone recommend a 500GB hard drive with an excellent cooling system and good reliability?
It doesn't matter if it's noticeably louder than poorly cooled drives, nor the size of the drive (I basically plan to park it at my desk and keep it there for its lifetime, so portability is not an issue), and it certainly doesn't matter if its read/write speeds are bad -- my computer only has a USB 2.0 port (no high-speed, firewire, or eSATA), so it wouldn't make much difference anyway.
EDIT: I forgot to mention: the drive does not need to come with any special backup software or capabilities, and that it should not be an SSD (too expensive).
I have always preferred to build my own external hard drives. You can buy a good caddy / enclosure for around £15-£20 ($24-$32) and then can pick a good quality drive also.
I'd suggest getting a WD Caviar Green 500GB drive as they are made for cooler operation and power saving, and then you can get a nice caddy with a small 40mm fan or whatever included. Comes out about the same price as a pre-made external, but you know it's quality inside.