Go to all the local bike shops and test ride their bikes. Find out what size is best for you. Remember that same size frames from different manufacturers fit differently. I have two bikes. Both 58's. One I test rode and it fits. The other was purchased off the internet and it is small. I have the seat post and an adjustable stem at their max height. It looks dorky, but the bike was a great price. You can learn from my lesson.

After riding their bikes for two hours, and using the salesman's time, tell them you want to buy a bike off the internet, then leave. It is good to be honest about your intentions. (just kidding - This presents an ethical conundrum.)