These things only exist in some sort of prototype phase but if the corporate entities of the world allow them to come to full fruition they could end up being pretty incredible:

• The Bloom Box - a power generator potent enough to provide enough energy for your entire home from a device roughly the size of a shoebox; completely disconnected from the grid. This is well beyond the realm of comprehension but I buy into it wholeheartedly. via Courtney.
• Lasers may enable fusion - while this may end up being as chased after as Cold Fusion it sounds like there is some serious headway being made on generating serious amounts of power with this laser technique.