Considering a pet door? Moore Pet Doors has a site that sells and exhaustively explains every type of pet door imaginable -- ones that fit in overhead-type garage doors, ones that can be installed in screens, "bite-guard" doors (for pets who chew on regular flap doors), heavy-duty plastic dual-flap doors, and our favorite, the raccoon-proof door ("Keeps out: Raccoons, snakes, rodents, opossums, skunks, alligators, monkeys, scorpions, other pets"). They also make custom pet doors, and replacement flaps.
And, for those of you with indoor cats who want to keep the cat box in a closet, the Cat Hole -- a very attractive wooden doorway with an optional brush attachment that, yes, grooms your kitty as it goes in and out.
We've installed, tried out, and modified cat doors for years, but I've never before come across such a comprehensive online catalog of doors, complete with ratings and reviews. (Speaking of which...we own the Solo raccoon-proof door, and I can testify that we have never yet had an alligator get into the house!)