As Saluki says above, what kind of riding do you intend doing? You need to work out if you intend to do, just road riding, commuting, off-roading or a mixture of each. This will give you a clearer path on which bikes to look into.
I'm 5'9 and about 240 pounds and have been riding a Whyte 801 for a couple of years for Off road and a Specailized Sectuer for about 6 years, and neither have given me any issues or sign that they cant cope. (The Sectuer, other than tubes and tyres is standard and has not needed any replacement parts because i have, for want of a better word, "Squashed" then by being to big!) The Sectuer is good for me as the relaxed geometary make it more comfortable than a full on race bike, and i can spend 3-4 hours very comfortably racking up the miles.
Its good to do a little research and asking questions here before you hand over any cash, but once you know the path your going down, get out there and enjoy the ride.