I was comparing the pricing of External drives and here are the results. Its Amazing to see how we used to talk in MBs, then GBs and now TBs.

GB 500 1000 (1TB) 1500 (1.5 TB) 2000 (2TB)
Price in US$ 73 95 135 200
Cost per GB 0.15 0.10 0.09 0.10

The cost per GB for two 1TB is the same as one 2TB. Unless you need more than 1TB which is a lot, I would buy a 1TB drive and keep the budget for another drive in the future. Who knows by the time you run out of your 1TB, you could get another 2TB a the same price.

The bottle neck will now be the data transfer, USB 2.0 is just not fast enough.. so look for eSATA. Your PC/Notebook should also have an eSATA port. A NAS box with Gigabit Ethernet would also be fast, provided your network card and your network is 1GBps.