Frame sizing is the seat-tube length. However, for better bike fitting, you should really concentrate on effective top-tube length. You may wish to visit some fitting websites and take some measurements of yourself. Then when looking at bikes, go to the manufacturer's websites and check out their geometry specifications (assuming they publish those) to see if you can get a good match. Of course the best way to see if a bike fits you is to actually attempt to ride it. You might want to hit a few LBSes and try test riding some bikes.