I bought a NANEU PRO Urban Gear U120 about 18 months ago, and have been very satisfied with it. Have a look at
this link and see what you think. It is OK to go in overhead lockers on planes (just), but I have not been refused in about 15 different check ins. Very well made, and considerably cheaper than the LowePro gear, or was 18 months ago. It has so many pockets and compartments that you need a GPS, or you'll get lost.
The really good thing is that the inner camera compartment lifts out completely, leaving you to use the back pack for trekking. It has a bottle holder, a tripod holder, CD player compartment as well as taking a 15" laptop. My gear all goes in. 40D + 18-75 lens fitted, a spare 300D body, 100-400 IS Zoom, 12-24 WA Zoom, 50mm standard, 100mm Macro, cards, batteries, cables, charger, cleaning gear, extension tubes, as well as my 15.4" laptop.