Your proportions, flexibility and intended use for the bike may have large impacts not only on what "size" will fit you, but, also on what "models" and/or "manufacturers" will best fit your needs.

I've used a number of the online fit calculators to assess both myself, my wife and a couple of our friends with some success. None of them are perfect, but, they provide an excellent starting point to get you in the ball park. Competitive Cyclist and Zinn's are two of my favorites. I like the fact that Competitive Cyclist provides three fit options ranging from fairly competitive to fairly comfortable for consideration.

If you take the time to get a friend or realative to measure you, these fit calculators can help identify which parameters may be most important to you and can provide a way to compare frames from different manufacturers whose stated sizes frequently vary greatly from one to the other.

I would love to be able to say that this is an area where an LBS offers great value. But, I can't. So far, the majority of times that I've walked into an LBS looking at bikes for myself or the Mrs. they have proceeded to attempt to sell what they have. Not once has a salesman suggested that we should investigate a brand/model they don't have on the floor. On several occassions, when they haven't had the correct size, they've pushed toward a model we weren't interested in because they did have the correct frame. I've had salesmen attempt to fit me on frames that were competely inappropriate for me.

Once you know what style and size of frame will work for you and have purchased such, the final fit can take place. That's going to be fine tuning saddle height, lateral location and angle, stem reach and height, bar angle, brake lever location, etc. If purchased new, from an LBS, this should be included as part of the initial sales service. Anticipate an hour to two for this.