Mud River certainly seems the most popular, although there are other brands out there for cheaper. Can't speak to their quality, but if you get a Mud River juts be careful putting the cover over the kennel as you can rip the bottom seam if you man handle it (ask me how I know...)
I live on the westside and the temps here rarely get to the point where I feel I really need to use it, but if I lived on the eastside I'd be getting an insulated one.