We bought an inexpensive Cosco Scenera for travel...very lightweight and relatively easy to schlep through the airport whether gate-checking or using in flight. <img alt="" class="inlineimg" src="http://www.mothering.com/discussions/images/smilies/winky.gif" style="border:0px solid;" title="Wink">
We have a backpack that fits our convertable seat. I think it came from diapers.com but they also have them at Walmart. It is big enough that we end up packing blankets and clothes in there (in mesh bags for easy re-packing around the seat upon arrival at the airport) too. DH or I can easily wear it through the airport while dealing with baby and other carryons. We label it clearly as a car seat and make sure that it is gate tagged so that we can check it for free. An added bonus is that this also somewhat protects the car seat.
We bought a large hockey bag with wheels for the carseat. It's got a structured back so I feel it does offer at least some protection to the carseat. We check it - no way I'm lugging anything extra through the airport - especially as we don't use a stroller so we're already carrying everything else & ds.
The simplest solution I've seen is <a href="http://www.amazon.com/gp/redirect.html?ie=UTF8&linkCode=ur2&camp=1789&creative=9325&tag=motheringhud-20&location=http%3A%2F%2Fwww.amazon.com%2FTraveling-Toddler-Seat-Travel-Accessory%2Fdp%2FB000JHN3AS%2Fref%3Dsr_1_fkmr0_1%3Fie%3DUTF8%26qid%3D1274279556%26sr%3D8-1-fkmr0" target="_blank">this little t-strap</a>. It fits over a wheeled suitcase and then you use the latch-system hooks on the car seat to hold the car seat firmly to the suitcase. Then you just wheel the thing along! No need for an extra bag or anything. I imagine you could just unhook it to bring it on as carry-on baggage if you want, as long as they let it on the plane.<br><br>
My friend was going to buy this, but instead we went to JoAnn fabric, picked out a set of D-rings and a length of nylon strap (total cost - less than $3), and she sewed it herself. Simple and brilliant!