If Apple brings Airport back into the Time Machine feature, you'll want to consider something that has USB connectivity if you want to connect it to your network and allow multiple machines (espeically laptops) to back up to the new drive.
Thats what i was thinking and i bought a 500gb lacie usb drive off amazon for $120.
Heres the link: http://www.amazon.com/gp/product/B000H6CBA4/102-2788430-0679314
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