1. Dedicated offline Ubuntu Live on USB drive.
2. Create a bunch of private keys offline and put them in a truecrypt container.
3. Backup the truecrypt container on multiple locations (both local and online).

This pretty much reduces the risk of theft or losing the money to ZERO percent.

For extra paranoia, e.g. in case of kidnapping your family and demanding the private keys as ransom:

4. Use a time-lock, i.e. a remotely controlled server that sends the passphrase for the truecrypt container only X days after you request it. Obviously this implies the inconvenience of not *instantly* being able to access your money, but that's the whole idea.

I don't think it gets any more secure than this.