Shipped to my area (Middle USA):
- WD Caviar 120GB, $63
- Maxtor QuickView 120GB, $69
- Seagate Barricuda 120GB, $68
- Seagate Barricuda 160GB, $70
- Maxtor Ultra 200GB, $88
- Maxtor DiamondMax9 200GB, $88
- Maxtor DiamondMax10 200GB, $86
- WD Caviar 200GB, $89
- Maxtor MaXLine Plus II 250GB, $92
- Maxtor DiamondMax16 250GB, $96
etc, etc, etc
Play around with the filters on the left column, and if you order from pricegrabber, be sure to pay attention to both shipping and vendor reviews. I've never had a problem with a vendor from them, but I've never ordered from one that I felt might be shady. YMMV.
I would highly recommend Seagate Barricudas. A lot of people recommend Western Digital and Maxtor, because they are some of the cheaper ones around.. but I've had problems with drives from them failing in the past. They've probably fixed them by now, but Seagate is rock solid.
EDIT: Don't forget to doublecheck that you can lock the drive if you play Xbox Live.