Hi Fatnewby
I am 240 pounds, but I started riding last year I was 275 pounds.
I have been riding a Trek 1000 (I bought it 2 years ago for $550) because it was cheap (I was not sure how seriuos I was going to be initially).
I feel my my own personel view is that big guys need aluminum since it is highly resistant to flex. I would recommend a Cannondale R500 or R800, just make sure you get strong wheels. My Trek 1000 is good, but in my opinion the Treks are over valued.
But it is really important for you to go to several bike shops and have them size you up with your dimensions and then test ride several bikes so you will get a better idea of what you can expect the bike will feel like for you. What will work for me may not work for you. I prefer the stiffness of aluminum so I can go fast, Carbon is very comfortable, but with my weight, it would flex a lot.