I'm going to suggest a few ideas that are off the beaten path. Besides buying and holding Bitcoin (which I think is a good bet over the long term):

1) Start a mining pool

Bitcoin mining is finished for the little guy. You need to prepay for expensive mining rigs that quickly stop being profitable once you finally take possession.

But almost all miners need to use a mining pool. Most pools look amateurish. Talk to Bitcoin miners and find out what they're missing and build it. You will get to skim a nice 2-3% off all the mining profits without investing in expensive mining hardware.

2) Lend money to Bitcoin traders

Don't have the stomach to risk your money by investing in Bitcoin? You can profit by lending your money to people who do.

Bitfinex.com allows you to do this. You can currently lend out USD at 200%+ APR to people who use it to buy Bitcoin on margin. The risk is low to nil as the loans are backed by the borrowers BTC and Bitfinex will close out their position and repay you if the value of their holdings drops too much.

Call me if you want to get feedback on your ideas.