Also Caroline Ekis runs a lot of tours as well to Antelope:http://www.antelopecanyon.com/
I have been there when it was snowing and it was still really nice, damp but nice. The rays of sunlight are a summer thing and that is also monsoon season and also very crowded. I prefer the winter months, more time to compose and spend in the canyons.
Another interesting slot in the area is Secret Canyon, and the tours there are run by:http://hummeradventures.net/tours
A friend and I went on the tour, off season and we were the only ones on the trip to the canyon, so we had it completely to our selves for several hours before the guide wanted to get back to town to pick up his next tour.