It has a small form, but the LaCie Little Big Disk Quadra packs 1TB of storage.
The Neil Poulton-designed Little Big Disk Quadra includes two 2.5-inch hard disks with 110MB/s burst transfer rates when using eSATA or up to 80MB/s if using FireWire 800. It's also fully plug and play with Mac OS X 10.5 Leopard (including Time Machine) and Windows Vista.
It's available now, with prices starting at £399.99
LaCie
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It's quite good for it's size but the lack of eSATA, and USB bus power is a turn off..