My two favorite brands are Clek and Diono. Diono Radian seats are ok for travel, since they fold, but they are HEAVY. Steel frame. Clek seats are quite big, so they wouldn't be great for plane travel, either. We used the previously mentioned Cosco Scenera for travel and have been using the Clek Foonf at home.

The nice thing about both the Clek Foonf and the Diono Radian seats is that they enable you to rear-face your child for a long time. It is recommended to rear-face at least until age 2 and optimally until they outgrow the rear-face limits of their seat. The Foonf has a rear-facing limit of 50 lbs and approx 42". My 4.5-year-old still rear-faces in his Foonf. Why rear-face? Statistics show that kids who do are five times less likely to die in an accident if they are rear-facing. The risk of serious injury, including internal decapitation from the vertebrae separating in the neck, is greatly reduced, as well.

Back to the Scenera... While it doesn't fold, it is so light weight at only about 8-8.5 lbs that you can easily hang it on your stroller handle as you roll to your gate.

car-seat.org is another great forum for advice on traveling with car seats. Definitely worth checking out.