Osprey makes a whole line of travel bags, pretty much all of which can be carried on (short of the full sized backpacking packs).
I use the farpoint 55, which is pretty big, but includes a detachable day pack that will fit a 15' laptop. I have never had any issue using it for carry on, and airlines don't seem to care much so long as it fits on your back and isn't enormous.
If you want something smaller, the Osprey farpoint and porter both come in smaller sizes, and I can recommend both without reservation. They are exceptional travel packs, and you should be able to find a configuration that works for your needs.
That said, I'm not sure I would call their aesthetics "conservative", although they do come in black and grey, and Osprey is a well respected brand if that matters.
I also hear good things about the Quasar, but don't have personal experience with it.