Well if energy is cheap and owned by FF, then some major markets are still available for investment:
1)Intelectual property
2)Manufacturing
3)Utilities
4)Raw materials
5)Commodities
6)Food production
something more?
Intelectual property is under attack from open source and piracy. While the second one might get reduced, the first one will get just worse.
Manufacturing will also become something you can do at home, in the long term. Look at the goals of http://www.reprap.org .
From the rest I would invest in Raw materials, as cheap energy should allow to get raw materials much cheaper, even those that are high in demand. For example you can get gold from salt water, its just not economical with current energy prices.
Utilities should be a good investment in the short term, as energy prices for the consumer wont fall very fast, and most of the profits will be collected there.
Commodities an Food production markets are overbooked IMHO, and cheap energy is not likelly to affect them fast. Of course in time prices will fall, after raw materials and energy become cheaper, but I would question the availability of profits there.
And of course you should want to invest into FF infrastructure development, that should be a gold mine in short term.
My 2c