Wow, I feel retarded...
My G-Drive Q does require AC power...I meant to link you here:
That one doesn't require any outside power, it is bus powered (FW or USB), and up to 500GB capacity, although USB might not power it then, you'd need firewire.
If you're really wanting something sick though, you could grab the G-Raid, up to 640GB capacity...put that in Raid-0 and you'd have a set set-up.
I'm not sure which stores carry them, you'd have to call around locally or shop online, I've never had a problem with mine, and it comes pre-formatted for Mac.