Pet rock, funny i went to grade school with the pet rock guy's daughter, he made truckloads on that, then lost all those truckloads all on this next big thing, which was so big no one remembers what it was.
I have 20 patents, and yes the vast majority have and will never directly generate money. patents are mostly something that established companies use to prevent entry of new companies into a given market. Each established company cross licences with all the others (they are all usually violating each other's patents). No one else can enter the market because they would be facing the wrath of all. So most ot the patents indirectly make money by gain access to other companies patents thru cross licenses.
do the initial patent search yourself here:
http://164.195.100.11/netahtml/search-adv.htm
the database only goes back to 1976, but its a good start
you can also go the non-disclosuer route. basically set up a meeting with the company you want to sell too. have them sign a legal document that they cannot disclose or use anything you show to them (that they don't already know) without your approval. This ends up being as good as a patent because unless they can prove they had been working on your idea, they can't do anything with it. If they can prove they had been working on it, in the US that would invalidate you patent anyway (US is first to invent, most of the rest of the world is first to file).
good luck,
jason