I just picked up a compact travel tripod, the Gitzo GT1541T, from Amazon. Made of carbon fiber, this is one of the lightest, smallest tripods you can find. This is not a full review, but I wanted to show how easily the 1541T fits in a standard 22" carryon bag. Although the bag is listed at 22", the usable interior length is only 19" - but the tripod fits with plenty of room to spare. The tripod is shown with the legs folded back over the center column.
Another size comparison, here's the tripod next to the Nikon D700 with 70-200mm - it's only a few inches longer. With the hood on the lens, they'd be about the same length exactly.
My intial impressions of this tripod are favorable but unfortunately it may be a little short for me. With a height of 45", it's not that comfortable for a 6 foot tall person, and extending the center column reduces your stability quite a bit.