I will have the same setup, do you have an external hard drive to recommend?
Depends on your budget.
If budget isn't a problem, you could go all-out and get a Promise Pegasus R6.
Otherwise, any USB 3.0 external drive will do you fine, considering that they've got a theoretical bus speed of 5 Gb/s.
Western Digital and Buffalo make good ones.
Oh and on second thoughts, without spending too much money, you could consider the Buffalo HD-PA1.0TU3 Thunderbolt 1TB drive. It can run on either USB or Thunderbolt. Read/writes are around 106-120MB/s.