Addendum added January 28, 2013: My vet had never noticed these carriers because I had never put one up on the exam table until my last vet visit. She looked at it with interest and totally concurred with my opinion of having a small, but open carrier for my two (panicky) cats. She has seen more than a few overheated pets in too enclosed carriers. Since I live far from the vet I always carry spare towels for the bottoms of the carriers and she found that the "stable floor covering'* I use was an additional comfort feature for my pets long trip to their appointments. (I just ordered the larger size of this carrier for my "Phat Kat" and will donate her previous carrier to our local animal shelter.)
After sorting through hundreds of models, interviewing dog experts, assembling the top models and lugging them to a veteran trainer for examination, and then trying to break each crate at its weakest points with measured force, we found that the MidWest Ultima Pro is the crate most people should get for their dog. It’s the most sturdy, secure, and adaptable wire crate we found, and it’s designed to last over the lifetime of many dogs. It’s also available in multiple sizes.
Features: The Midwest Homes for Pets Ginormous Crate measures a whopping 54 inches long, 37 inches wide and 45 inches tall, making it big enough for most Great Danes, Irish wolfhounds, mastiffs and other big breeds. The Ginormous Dog Crate is a wire-style crate, that uses special L-bars to prevent the sides from bowing out the way they do with some crates.
Update: We traveled quite a bit this holiday season and this portable crate was absolutely awesome! I have seen some reviews about bad zippers but suspect it's due to misuse. You have to raise each side before zipping it -- just common sense, people. Otherwise, there is too much pressure on the zipper. I think zippers on this crate are sturdy. Another suggestion is placing your dog's favorite bed inside. The crate (we have extra large) has plenty of room to add an extra large fluffy dog bed our dog loves. Because the crate folds flat, we place the crate in the cargo area and cover it with dog's bed when on the road. The dog sprawls like a queen! :) When we get to the destination, we unfold the crate, throw the bed inside, and voila -- cozy house that ... full review