Hydroelectric was brought up and then put back down with the 'most of the dams that can be built in the US to any great effect have been built'.

there's one in my hometown (we also have a nuclear power plant). When they built the dam, they created Lake Dardanelle and displaced quite a few people; there's roads leading into water that I never knew about until my dad pointed them out.

(of course the lake gets a lot of recreational use, and I'm sure they reimbursed the people that had to move, but it's kinda creepy to think of a lost city underwater)

I like windmills. some day I'm going to get my dad to invest in some to put up at the house. he's always wanted to, but balked at the up-front cost.