If you are looking to "invest" your bitcoin then your best bet is most likely going to be exchanges like bitfinex, poloinex and possibly okcoin (which apparently has some kind of insurance-like fund to protect lenders).
You will essentially be making peer-to-peer margin loans and the exchanges' risk management system will (attempt to) protect you against defaults as the exchange will force-liquidate the borrower's positions if markets turn against them too much.
You will need to trust the exchange with your coins and you need to trust that market volatility will not be too great because if it is too high then the people borrowing your coins may not be able to repay and if this happens to enough borrowers, the exchange may become insolvent.
Bing, another business idea, bitcoin insurance
I believe the insurance works something like this (on okpay):
If the lender chooses to buy "insurance" then a certain percentage of the interest he is due will be paid into an insurance fund that will cover losses up to the amount in the insurance fund in the event that the borrower they lend to ends up having negative equity in their margin account and is unable to repay what they borrow.
I understand that okcoin's insurance fund is currently somewhere in the area of ~900
BTC, however the problem is that in periods of extreme volatility, if a lot of accounts receive margin calls, then there may be a cascade effect that causes many people to sell (or buy, depending on the direction of the market), which may cause ever increasingly large losses for margin traders.
