Thought I'd toss this in.

The three richest men in Australia (all billionaires) are involved in the following industries...

Media - Network TV and Multiple Newspaper Owner (repeat advertising sales)
Real Estate - Shopping Centre Chain Owner (repeat lease payments)
Packaging - Cardboard Boxes (repeat sales of boxes other manufacturers put stuff in)

As a side note... I bet EVERY member of the Young Presidents Organization http://www.ypo.org/ owns a business that involves repeat sales.