Kickstarter-like - back projects without actually owning the company, but you get rewards which might be a share of the profits. Can fund new BTC ventures
Several such projects already exist. They aren't very active, though. I guess the problem lies in trust, or lack of thereof.
Basically, organizer needs to be really serious about it, and he needs to find some serious projects.
Decentralized trading: A site that uses cryptography to verify the ownership of items. People can then trade them on IRC, forums, etc. Offerbook so you can easily find a buyer / seller.
This can be done using smart property/colored coins. There is no need for a site as ownership can be securely identified by client software.
A web site could, perhaps, act as a directory, i.e. a place where people can find information on particular property/coins.