I ride my old Trek 2100, modified so that I can carry a bit of weight, when needed. Had a double many years ago, it now has a triple. Had 700 x 23 cc wheels. Now has 28's (a tight fit, but doable, as long as I inflate the tires AFTER I put the wheel in the quick release.) No attachments for panniers, but I have a decent rear rack with a trunk bag. I can at least fit summer work clothes in it...... When I need more room, I pull a BOB trailer behind the bike. I am hoping -keep your fingers crossed for me - that I will soon be able to purchase a used Cannondale T800 at a great price. I'd love to have a true touring bike, but seriously cannot afford to buy a new one. So if the C-Dale fits, at $350, I don't think I can pass it up. I can always upgrade components someday, if I feel its needed.
Anyway, I guess my point here is basically that you can make quite a few bikes work as commuter bikes. I love my BOB trailer, but sometimes it is overkill, and I'd be better off with panniers. You need to consider if you will use the bike primarily for commuting, or will this be a bike for all-around use? An option that I haven't heard mentioned yet would be a cyclocross bike. They won't haul the weight that a dedicated touring bike can carry, but for commuting, especially if you have rough roads/trails, it could be the right solution.
Lots to consider! Good luck!
annie
Time is a companion that goes with us on a journey. It reminds us to cherish each moment, because it will never come again. What we leave behind is not as important as how we have lived." Captain Jean Luc Picard