If you have 6.5k, go for Western Digital Caviar Black 1Tb HDD. This one's superfast but only available at a high price
option 2: Go for WD caviar green or seagate 7200.12 1Tb HDD for 4.5k
option 3: Go for two 500Gb Seagate/WD HDDs, each one 2.7k. This one reduces the risk of data loss. After all 1Tb is lot of data.