There is no comprehensive list of existing plants that I know of, except the one being worked up by Sierra Club and Synapse. The list of all proposed plants is available at http://www.sierraclub.org/environmentallaw/coal/plantlist.asp

I would recommend going to either the EIA or EPA (clean air markets data) sites to find existing, but these require doing some searching to limit the plants to coal.

Clean Air Markets Data
http://camddataandmaps.epa.gov/gdm/

Sourcewatch has attempted to do this. If you click on a state on their map, a wikipedia type entry comes up and you can click on existing plants and get a google map and listing of capacity.

http://www.sourcewatch.org/index.php?title=State-by-State_Guide_to_Information_on_Coal_in_the_United_States