yes, the ocean.
though the combination of gravity effects from the moon and other large bodies and its own mass and volume, it is one of the great resources of energy that remains mostly untapped. clean and renewable, power obtained from the ocean could easily power the entire planet several times over with just a fraction of its potential energy.
of course, great care and attention must be made towards the possible problems that could be produced. it carries much of the same concerns of any other power source, though it is massively better than any non-renewable resource. if too much power is drawn from the waves at any one point, it could change the balance of the ecosystem of an area. this power source should be used in tandem with the numerous other renewable resources such as wind, solar and refuse/waste/recycled power.
as with many other renewable energy technologies, corrupt governments and corporations have historically used their power unethically and illegally to hinder and stop progress in the research and development of ocean power. Salter's Duck is a prime example. in the 1974, Professor Stephen Salter at Edinburgh University developed a brilliantly simple method of harvesting the energy of waves. it was proven to be cheaper in both cost and production than even nuclear energy with just a prototype. corrupt government officials and corporations worked tirelessly to spread LIES about his wonderful invention. he and his team fought for over a decade, until they ultimately disbanded due to the sheer power of the corrupt entities.
now a new generation of ocean power entrepreneurs have taken the challenge, with some excellent results and successes. Marine Current Turbines, led by the technology and vision of Peter Fraenkel, is a company based in Bristol, UK. their SeaGen uses what is essentially underwater windmills to generate power. they already have one in use in Northern Ireland, generating 1 MW by itself.
though Pelamis Wave Power has met its share of problems due to investors feeling the brunt of a poor global economy, this is technology that is definitely worth a look as well. it uses a technology that resembles a jointed 'snake', where the movement caused by waves is converted to power.
remember, seek the TRUTH.