I stand 5'11" with a 34" inseam (standover, not pant length) so most charts put me at a 52-54cm frame, but as mentioned above so much more comes into play. My touring bike is a 54 cm (21 inch) Trek 700 frame with a slightly setback seatpost and a 90mm stem with a 30-degree upward angle (flatbar) and it fits me perfectly as a touring or general purpose commuter. I also have a trail bike based on a Trek 700 frame but with a 47 cm (18.5 inch) frame a more setback seatpost, 110 mm stem and a 1 inch rise and slight sweep to the bar. This gives me a more upright position, excellent for standing while making tight corners. Still pretty comfortable, I rode it 18 miles of mixed paved and gravel the other day with no complaint, but wouldn't be my first choice for touring and it's definately not a road bike. Makes a good cruiser/commuter though.

I've tried many road, touring, hybrids and hardtails and can say that the "ideal" size for me falls over a several cm range depending on geometry, set up, and intended riding style.