Check out Kelty's Carport ($330, kelty.com). This minimalist, streamlined, three-season tent attaches to either the side or rear of a roof rack on an SUV or mini-van and, with its clip-sleeve construction, can be set up in a flash. With three mesh windows and full-coverage retractable side panels the Carport almost feels like a tent, except it's missing the floor. (Land Rover is sold separately.)
If you travel with a lot of baggage (or children), try the McMansion of attachable tents, the Napier Sportz SUV 83000 ($330, sportzbynapier.com). Napier isn't kidding when they say this tent transforms your SUV or minivan into a home away from home. With a removable sleeve and screen room, the tent wraps your vehicle with a 10-foot by 10-foot domed sleeping area for up to six people and a 7-foot by six-foot dining area. Coolest aspect: The car-attachment is removable, so you can roll away without worrying about the portable palace crumbling down.