This seems to be the most popular suggestion. Does anyone travel with one, though? I've found a local store that sells them, and I'm going to pay one a visit this week to see what they actually look like and how one would pack in a generally full carry-on.

The water temperature is a concern, though. The general consensus, and I'd agree, is that the in-room coffee brewers that don't make good coffee also wouldn't make water that's hot enough. An immersion heater seems to be the solution here. That doesn't take up much room, but it requires something solid to contain the water while heating. (Yes, I tried using it with a styrofoam cup full of water once) I usually carry a heavy glass cup (least likely one I have to break) and it doesn't really take up significant room since I can stuff a pair of socks inside.

Using the cup I'm going to drink from for heating the water for brewing with, say, a filter funnel, is a problem. It usually takes two pours of water to get a cup of coffee and that won't work when the cup for the hot water and the finished coffee are the same. A French press or the Aeropress, it seems, would not have this problem so this seems to be the best solution so far.