I've heard the Easy Tote is a good one, but have no first-hand knowledge. Not sure about the ones with wheels as I've seen one with broken wheels at the airport and it ripped the bag too.
This is the one we have: http://www.rightstart.com/global/store/product~item~884~dept~travel~cat~travel+accessories.html
Love, love, love it! DH didn't want to get one for our first vacation, thought it would be a waste of money. Thought he'd just put the cars seat on the stroller and have DS walk to the plane (or one of us carry him and the other push the stroller/seat combo). In the end he was glad that we got it! Made things way easier than he had anticipated.
For our last trip, it was one of the first things out of storage. All of our luggage hooks together with straps, and DH just slips one of the straps through the handle and attaches it to the end of the luggage "train." Also made it easier to get DS's blanket and stuffed animal safely to the plane. Just put them on the seat and zipped them in. No more worries! We have also checked it as luggage with no problems.
I bought the Eddie Bauer car seat bag for our WDW trip last fall based on the recommendations from the disboards. It's big and was only about $20. No wheels on it though.