Over the long (Thanksgiving) weekend, I made major updates to my A* pages for the first time in years. So far I've rewritten and added lots of diagrams to the A-Star Introduction and A-Star Heuristics pages.
The economic model in Railroad Tycoon 3 looks pretty interesting. (I'd link to it but I can't find a site that I can view. It all seems to be Flash. Ick.) Each product has a price at each spot of the map. You can view the map, click on a product, and see green for high prices, yellow for medium prices, and red for low prices. Without any players, the price differentials lead local transporters (by river and over land) to transport goods from one place to another. The players can come in and do this more efficiently, by investing in rail lines. Your job is to find products that you can buy at low prices (typically, but not always, where they're being produced) and sell at high prices. A few years ago I had wanted to write a game like this but never got around to it.
In addition to transporting goods, you can create your own goods. You have to build a factory (or other building) that takes raw materials and produces another good. By building factories, you can create supply and demand. From what I've read on message boards, you have to do this to master the game.
There's a free demo available of Railroad Tycoon 3. I've been playing with it a bit.