I know you said you wanted a roller, but I have become very apprehensive about any bags that fit in the overhead. If you get on and all the overheads are full, you are in deep trouble! I currently own a Think Tank Airport Acceleration 2.0, which is a fantastic carry on. It holds a massive amount of gear, and fits in the overhead perfectly. Think Tank bags are the best out there in my opinion. I wanted to get a backpack that would fit under the seat in case the overheads were full. I purchased a think tank Street Walker Pro, this is the gear I have in it, Canon 40D with a Canon 100-400L IS
lens mounted, with the lens hood in the reverse position, another 40D with a Canon 70-300L IS
mounted with the lens hood mounted in the reverse position, a Canon 24-105 lens, battery charger, scanner, extra CF cards, and batteries. Amazing what you can fit in this backpack, and it will fit under the seat.