Specifically, on a USB stick in a regular old safe-deposit box. Now your money is in a bank.

Unless the computer you used to move it to the USB was compromised in which case someone could still steal it.

Use a Live CD with a lightweight client that doesn't need to download the entire blockchain. Keep the wallet on a separate USB key so you can keep any generated change addresses (since a LiveCD is read-only). This should be pretty effective unless the hardware itself is compromised.. If you're worried about the machine being exploited while online performing the transaction, you could limit exposure somewhat by generating an offline transaction.