Packing for a trip can be a bit of a nightmare depending on the airline that you pick. Carry-on luggage is now limited by the airlines and the exact restrictions vary between airlines. Generally they limit the height of a carry-on bag to 22″ but there may be exceptions. Check with your chosen airline. Some travelers like the author of this article has a different piece of carry-on luggage for the three different airlines that he flies: United, Continental and American Airlines. Travelpro has a wide assortment of bags that generally fit the restrictions of any airline.
The author has a lot of good information on the entire subject.