I am 6'8" and 250 lbs. and find that for tall riders, Dutch bikes are the best value proposition. I currently ride a Batavus Stabilo with a 70 cm frame bought eight years ago. Unfortunately, Batavus is no longer imported into North America.
My next bike will be an Azor Pastoorfiets cross-frame bike. They come in sizes up to 73 cm and have a very upright riding position. In other words, you won't be hunched over. The crossframe also makes the bike much more stable for a tall and heavy rider. My Batavus has a crossframe as well, and I am commuting with it whenever the weather is above freezing.
Here is a link to a Canadian store that sells them:
http://www.urkai.com/portfolios/pastoorfiets-by-azor/The cost would likely be around $2,000, but I find that Dutch bikes stand up to daily commuting quite well. They have internal hub gears and a fully enclosed chaincase, which makes them much more practical than a mountain bike. To me, mountain bikes have always been the bicycle equivalent of full-size pickup trucks - style over substance, and not really that practical on a day-to-day basis.