Little Darwin

Since you are angled toward road riding, I would throw in another vote for the Trek FX line. I ride a 7.2 FX that I bought at the start of last season, and I weighed over 300 for the whole time.

No problems whatsoever with the bike, and the riding position is a little less upright than bikes with a "comfort" geometry, so you don't catch too much wind.

But to be honest, I would follow the suggestions above and go try a few. I wouldn't go for something that was too aggressive and hope to condition into it, at least to the point where you think you will be happy with it forever. However, I wouldn't hesitate to get one that was slightly too aggressive... since it will last longer before you feel compelled to upgrade. And then it would be a decent second bike for times you just want to cruise.

With all of that said, I would also check out some road bikes. As long as you are comfortable on the hoods or flats, I wouldn't worry about how you feel in the drops, since when I migrate to a drop bar bike, I don't expect to spend much time in the drops anyway. Even distance racers spend very little time in the drops, so you don't have to assume that the droops are where you should be riding most of the time. In my youth, I figured that the hoods/flats were good as a break from the drops where I usually rode. I am over that completely. For some road bikes, the hoods/flats could be roughly the same position as a road oriented flat bar bike. For road bikes, I would ask to see relaxed road, touring or cyclocross bikes (the latter 2 usually accommodate wider tires).