Vote for this proposal here
An in-game stock market is imho a great way to stimulate the SL economy and increase developer incentive while removing the benefits of installing camp chairs -- more money (and account stipends) can be pooled into a fully in-game funding market which directly helps companies grow, and ensures incentive to produce meaningful content. Of course, the design is not a trivial task, but I humbly submit the belief that the concept is very doable.
My own rough-draft scenario (as my less-than-professional skills and understanding would come up with) goes something like this: To ensure that this money is used effectively, companies could be partially managed in-game, where each company has an inventory and L$ account with a permission system similar to land-ownership, where anyone can add funds or items to the inventory and/or finances, but once an item is transfered, copied, or bought with the company money, it stays property of the company and the company owner. The spending/buying/trading history of the company is stored as the company's public record. Un order to gain the trust of investors, you already need to have some clout as a business and show that there aren't any "shady" transactions in your public record (this also ensures that if someone does attempt to cash out on the company, (say a decrease in worth/quantity of objects/money/stock or some combination is greater than a set limit, then a lock is placed until stock owners and/or Linden can take action and/or approve ... and limits to investing can also be placed ... this way, only two new abuses would be added to the list, and both would also be on public record. Additional benefits could be given for companies that increase profits (with various methods to test profit increase, such as the number of differing individuals trading with the company/etc -- these benefits could be decreased cost of land, increase in prim count per land, etc ... )
As the company finances increase or decrease in value, a percentage of the changes would go directly/automatically into stock worth. Furthermore, limits and permissions to amounts by sub-owners/co-owners could be options available to the original owners -- essentially, it's a mix between the SL "group", the standard "guild" found in MMORPGs, and the stock market.
That's my basic, ugly, buggy rough draft idea. I'm sure there are more effective and safer ideas, but overall, it would put a lot more control, incentive, and productivity into the hands of developers and business-owners, and provide a beneficial pooling area of Lindens from the SL economy as a whole.