I strongly recommend western digital hard drives they’re good quality and reliable over longer periods of time in comparison to cheaper alternatives, if you need it for storage than you can buy one that you connect to your pc through a usb port, however if you want to run your external hard drive almost as fast as an internal one, buy one that you can connect through a firewire port(more expensive), this means faster transfer rates compared to usb (however first make sure that your pc has a firewire port) – for example Im a video editor and I capture my footage into my external hard drive and through firewire I edit my footage as if it were on my internal hard drive.

Check ebay. I bought a 1TB external HDD off there for like 90 dollars and it works well.