There's been a ton of stuff written about this, and it's debated endlessly on every cycling Web site. Competitive Cyclist is a good place to start, though in my experience it tends to put you (well, me) on a frame that's a size or so too small. I had better luck following Grant Petersen's recommendations at Rivendell (www.rivbike.com), though he only promises that they'll work for his bikes. I'm not convinced the current trend toward smaller (and supposedly lighter and stiffer) frames is a good idea for recreational riders, especially geezers like me. I rode for years on 62cm and even a few 60cm frames because that's what the formulas said I needed (and it's also the largest size most shops stock). Rivendell's guide put me on a 65. I was nervous about going that big, but it was instantly more comfortable than a bike i'd had for years and really liked.
On the other hand, I'm in my 60s and just ride around. If you want to go fast, maybe not.