Montessori Today is the Polk book that gives an account of what it's like to go hang out in a classroom. Our library has a copy of it...you might see what all your local library has on Montessori.
One of my favorites is Children Who Are Not Yet Peaceful. Can't remember the author (our library does NOT have it, unfortunately). After I read it I was ready to move to Texas and enroll in the author's school!
Some of MMs works are available for free online. I'm not big on reading books online, so I don't have the addy at my fingertips, but if anyone wants it I'll find it.
edited to give the correct Polk book title, since all the Montessori books are starting to meld in my mind....