How do I know what size bike I need? If the LBS isn't all that helpful, and betrayed my trust, what are some rules to go by?

I am slightly over 6'3", and 6'4" with shoes. I tried following Shelden Browns advice when adjusting my seatpost for height, and it is high up there. I am wondering if I bought the wrong size, and which size should I consider on my next bike purchase.