The development of nuclear power was a really great start. But sooner than later, researchers realized it is not feasible, as it releases dangerous radiation. But a natural phenomenon known as sonoluminescence could allow us to duplicate the power of the stars. Until then, we still have solar panels as a clean way to produce energy.
Wind power catches up, but it is still not considered as a reliable energy source due to high maintenance costs. Furthermore, there is the ocean thermal energy conversion and the ongoing development of hydrogen fuel cells.
Looking further into the future, antimatter could also be viable solution. Research on antimatter is a priority, as it could provide us with much of the power we need. Too bad that it is very little of it in the universe – but it can be produced in laboratories.