Ironically, I had just ordered a new 2TB hard drive on the day you sent your message. I got a Western Digital My Passport Studio portable drive with USB and two Firewire 800 ports. I like the fact that it has two Firewire ports so I can put it in a daisy chain with my existing LaCie Firewire drive. My computer does have Thunderbolt, but Thunderbolt drives are a good bit more expensive. I also need the ability to move this drive between home and school. Not all of the school computers have Thunderbolt but they all have either USB or Firewire.
This particular drive comes formatted for Mac (HFS+). You can use any drive with your Mac, but you may have to reformat it if it's set up for Windows.
The drive was $199 at NewEgg and includes both the USB and Firewire cables, which saves you a few bucks. Many drives don't include the cable(s). I noticed in my shopping that you can easily find a 2TB drive for under $100 if you get one with just a USB 2.0 connection.
As for backups, I have the external LaCie drive plus a subscription to Carbonite for an offsite/cloud backup. I also burn DVD's periodically, although I'm long overdue. Can never have too many backups. This new drive is specifically for a bunch of videos I'm recording for school.