Oil rigs are pretty utilitarian structures, but once they've pumped all the oil they're going to pump, they become useless hunks of metal. If that seems more than a little wasteful to you -- not to mention an eyesore, considering how many rigs are within sight of shore -- you're not alone. But not to worry: industrious Ecogeeks are coming up with all sorts of ways to repurpose old rigs.

Dive sites

In this case, you don't need to do anything; the underwater support structures of oil rigs become artificial reefs on their own. There's one of these not far from my house in LA that's popular with divers called Oil Platform Grace, which has been inactive for years (but still serves as a pumping station). It was actually the site of a pretty nasty oil spill in its early years, but now all 320 feet of its underwater supports are teeming with fascinating life.

Wind turbine platforms

Winds are high offshore, so it's a great place to harvest wind energy. Only problem is, it's much more difficult to build turbines in the water than on land ... unless you happen to have a disused oil platform around! A company called SeaEnergy Renewables is planning on doing just this. Pretty cool, right?

Luxury offshore hotel

The winner of this year's Radical Innovation in Hospitality award sees old oil rigs in a whole new way: as places to build luxury hotels. It would still have a wind turbine, but its function would be to power the hotel, which would include more than 300 luxury suites, a conference center, a rooftop infinity pool, a diving bell (of course), and a casino. (Hey, as long as we're offshore ... ) It may not be the most eco-friendly way of repurposing of an oil rig platform I've ever seen -- just ferrying guests to and from the hotel alone would eat up more resources than the wind turbine would likely generate -- but it's certainly the most interesting.