Generally for starting off, since you are a bigger guy guy, I would probably recommend a steel bike. Steel bikes are very strong and very comfortable to ride. They are usually cheaper than CF or Titanium. I think Ti is probably one of the strongest, and CF is very strong too, but they are both very expensive since they generally weigh much less.
If you like to build, there are lots of older steel frames out there, that you can build up the way you want. I have an older 1989 Centurion Expert Ironman, in a 60cm frame (22.5#), and it could easily handle a 230lb rider, as I was 210# when I started off, and she is a real strong bike. The nice thing about the frame is the 700c design allows me to upgrade to some newer components if I want to.
If you are just starting off, you might want to do that, or even talk to the LBS about whether they can get ahold of an older used one for you. They are usually more than happy to help, unless they try to pitch something they have, you might want to be careful there. But usually, they will be more than willing to work with you.

For starting off, I have always felt steel bikes are really some of the best, because they are stronger than Aluminum, and are a little smoother to ride (usually). Plus, if you turn out not liking it, then you haven't lost too much money.

Check out Ebay, they have some great deals on older steel bikes all the time.