This is what our local pet rescue shelter uses (as well as our town shelter). We had one for our last pup, but she was quite destructive and eventually clawed at it and ate it to pieces. I would recommend it (our lab was just extra destructive).
It did a good job of keeping her cool in the summer (it was over the concrete floor so the coolness seemed to radiate up, and in the winter we put a thick fleece-covered memory foam pad on it.
http://kuranda.com/donate