[Rain Man]

I'd probably do something like this:

$20 million in income-producing real estate of the most conservative kind possible, scattered around the country
$10 million in money markets and other conservative, conservative U.S. bank accounts.
$10 million in my house and other hard assets
$10 million in T-Bills and stuff
$10 million in cash in safety deposit boxes and buried holes in the ground
$10 million in conservative U.S. mutual funds
$5 million in bonds
$5 million in money markets and other conservative, conservative non-U.S. bank accounts.
$5 million in conservative foreign mutual funds
$5 million in gold
$5 million in high-value art and other collectibles
$5 million in moderate to aggressive U.S. mutual funds