I have multiple hard drives, video work basically requires it lol.
I have a G-Drive 2TB HD that I store my iPhoto Library and completed video projects for YouTube on, and a 500GB Seagate Slim that I put completed work projects on.
I must say that you get what you pay for when buying a HD, Western Digital and Toshiba are not the best brands to go with, I only use the Seagate because it's projects that I will likely never touch again, but want to keep around just in case.
I have also used a 1TB LaCie HD that was very good, fast and quiet.
A really good HD will have you looking at around $150+ generally, a $50-$90 HD will probably break within 1-3 years.
EDIT: Buying a more expensive HD will also get you faster transfer rates, which means less time sitting around doing nothing while your computer copies files to and from the HD.
The difference is day and night between my G-Drive and my Seagate. especially when you are moving 10+ GB's around often - more than once every few months.