By recommendation of a weatherization consultant (who is fortunately a neighbor of mine), I insulated my crawlspace this winter. The walls were done with four inches of foam sheeting Since the floor above the crawlspace is living space, I did not need to insulate the ceiling. Also, I removed the window between the crawlspace and the basement and omitted insulating that wall.
What I did NOT do was insulate the floors. I read up on it and asked my neighbor, his reply was "I wouldn't bother". I did, however, take spray foam and seal all the spaces between foam board and the floor, as well as fill in any cracks in the floor.
Like the other guys are saying here, the money would be best spent addressing the attic and all the other places where heat escapes.