In Columbus, Ohio there is an old garbage dump that they sealed up with soil and vegetation. Some type of pump was placed above it and they're using the carbon monoxide emissions as a power source. Seems to me that more cities should do this.

In the same vein, Cincinnati has a humongous land fill that has been named Mt. Rumpke (Rumpke is the trash/recycling company). I've not seen the dump personally, but apparently it's quite big - big enough that they could seal it up and use it as a ski slope (with fake snow) and get energy at the same time!