I can tell you what NOT to get. Don't get a Maxtor OneTouch 4. The case has next to no ventilation, and fits tightly around the drive. This causes the drive to run smoking hot.
This is ok for occasional use, like using it for an hour once a week to backup your PC, but is horrible for a DVR, especially when used as the main recording drive, like on a ViP 211.
I had one laying around and began using it as a DVR drive on a 211, and quickly found it was running way too hot. I took the drive out and put it in an Antec Veris case and all was well. When I needed another USB drive for a different 211, I found an old WD 250GB drive that I was willing to sacrifice, and put it in the Maxtor One Touch 4 case. It took all of about two days to cook the drive and destroy it.