I've always used LaCie external hard drives. However, LaCie doesn't actually make the drives, the three I have are Toshiba, Seagate and Samsung. Given that, I've had very good results with all of them and I've had multiples of the Toshiba and Seagate, 2.5" and 3.5", PATA and SATA. Some people like Western Digital but I've always had better results with either Seagate or Samsung like I said.
Here are some drives I recommend. LaCie Desktop Hard Drive - 1TB - USB 2.0 (1 DISK) - $100 LaCie Grand - 1TB - USB 2.0 (1 DISK) - $90 LaCie Grand - 2TB - USB 2.0 (1 DISK) - $140
Regardless of the price discrepancy, I'd recommend two of the smaller drives. I also don't recommend getting drives that actually contain two hard drives but act as one. The problem with these drives is that if one of the internal drives fails, all of the data is lost. Personally, 2TB drives are so new that I'd recommend getting a couple 1TB. If you don't want to go with LaCie, here are some alternatives. Samsung Story Station Plus - 1.5TB - USB 2.0 - eSATA (1 DISK) - $120 Samsung Story Station Plus - 1TB - USB 2.0 - eSATA (1 DISK) - $110
You can get a samsung story 2TB for $140 but personally I don't trust the 2TB drives, they're too new. If you want a western digital, they're fairly cheap as well. Western Digital Elements - 1.5TB - USB 2.0 (1 DISK) - $120 Western Digital MyBook Essential - 1.5TB - USB 2.0 (1 DISK) - $130