I've got a Seagate 1TB external and a Western Digital 650GB External. Both work perfectly and spend their time hooked up to my torrent box and are on and being used 24/7. So far the Western Digital is 2 years old, and the Seagate is 1 year old (both were Black Friday deals), and they still work great.
Basically what you're going to want to decide is whether you want a portable drive, which is usually a laptop drive in an external enclosure powered by USB, or an external drive, which requires a power supply. If you want to take it places and aren't as worried about speed, go for the portable. If you just need a lot of cheap, fast, external storage for your movies on one computer, get the standard external.