Here is the URL to the clydesdale section:
http://www.bikeforums.net/forumdisplay.php?f=248
If you look at the post towards the top, "Clydesdale index thread", by one of our more thoughtful regulars, a guy named Air, you'll see that he spent a lot of time picking out jewels about bikes for us big guys. (That he picked some of my ramblings is not an endictment of him, I just happened to have posted when he was doing it. The helpful stuff I post I am usually plagerizing somebody smarter than me. (
http://www.bikeforums.net/showthread.php?t=228851 will get you there too.))
I'll say this, I'm also over 300 pounds. (By 6.8 fewer pounds this week than last but still over none-the-less.) The most important thing is your wheels.
Where are you riding, what are you looking to do (short and long term) and how much do you want to invest?
Read some of those posts and answer those three questions. Then come back, we are a pretty helpful bunch.