One, David Fokos, is a Massachusetts-based photographer who takes very long exposure large format prints usually of water. His gelatin prints have to be seen to be believed... here's an example:

Another, Tokihiro Sato, also takes long exposures. His collection is called "Breathing Light". How cool is this??:

Another of my favorites is Richard Misrach, whom I was very fortunate to meet because I went to school with his son.