presidential bios

After reading the very informative threads on the Best Presidents and Best VEEPs over in Great Debates, I’ve concluded that I really should know more about the US Presidents.

I prefer reading biographies as my entry into historical studies. Does anyone have any suggestions for good, one-volume biographies of the various presidents, acessible to the general reader, rather than aimed at academe, and interesting to read?

(I realise that for some of the Presidents, like Fillmore and Pierce, there may not be any bios that fit these parameters, but I think I can live with not knowing a great deal about them.)

Any and all suggestions welcome.

The Personal Memoirs of U.S. Grant is available online for free here:

Volume 1 - http://www.gutenberg.net/_authors/redirect.cgi?site=mu&dir=97&file=1musg10&ext=txt

Volume 2 - http://www.gutenberg.net/_authors/redirect.cgi?site=mu&dir=97&file=2musg10&ext=txt

Grant admittedly tended to focus on his Civil War military career, but that was arguably the best part of his life.