I am with everyone else on the "take a carseat" advice. Dh and I have traveled extensively with my 2 1/2 yr old son, and we found the absolute greatest invention in the world. It's a FAA-approved, five point harness, carseat that converts into a stroller. It can be used rear facing for babies as young as five pounds or forward facing for kids up to 40 pounds.
The key is, the wheels and handle retract so it fits in a plane seat (or backseat of a car) just like any other carseat. But then, when you are ready to move, just lift it out of the seat (with the child still strapped in), pop up the handle and the wheels come down and you have a stroller.
We love it b/c we can put our son in it at our house, drive to the airport, maneuvere our way from parking lot, through our hometown airport, roll him right down the aisle of the plane to our seat, then same thing when we land -- his feet literally never have to touch the ground. (Altho we do let the little guy stretch his legs now and then LOL) We are besiged by other traveling parents everywhere we go with it ... if I had a dollar for every time we've been stopped in an airport by someone wanting to know where we got it, I'd be rich!
Speaking of dollars -- it is pricey (about $160) but if you are thinking of traveling very much at all, it is SO worth it. Or, you can do what we did, which was split the cost w/ another family. (But now we just can't travel at the same time!)
We got ours from RightStart, but I've seen them in other kids catalogs as well. Here's the link to it on RightStart:
http://www.rightstart.com/global/store/product_detail.cfm?TID=09614646215335620112036275&Site=baby&rs_section=keywordsearch&GroupID=2281&GroupTP=Model
Good luck and happy flying!
~HenryMom