http://www.bsn.com/Cycling/cranks.html
by the way, their calculator ain't working.
I like this quote, even though the article seems to be kinda old, and I've just bought 2 pairs of 180s:
"
If you look at elite cyclists, despite an increasing number of long femured (tall) competitors, you will see that 175mm is pretty much the longest crank (other than for time trials) that is used. I would not, as has often been suggested, put this to conservatism. On the contrary, the fierce competition and prizes of professional cycling are substantial and bring a willingness to quickly adopt what might appear to provide some form of advantage -- which more often than not is at best psychological. In a realm where high tech voodoo and strange science abound, I can't accept the arguments to the contrary...
Ya gotta admit, this sounds more than reasonable. Despite the image that Euro cycling is sometimes smothered by tradition and conservatism, like he said, if the riders thought they would get an advantage from long cranks, I reckon there'd be more using them.