Which energy sources seem most likely to be used in the future?

Nuclear is definitely going to be present, as will hydroelectric, both of which are already well established, wind power is already becoming popular and a great deal of research is being focused of solar energy. Another hopeful is the harnessing of tidal action and waves.

The holy grail of future power production is a commercially viable fusion reactor, the realization of which could be just around the corner or decades away. The JET fusion experiment managed to produce 16MW of power, 65% of the power used to start the fusion reaction.