Montessori Schools

Early Years Montessori (note that there is also a different school called Early Years Preschool)
Full Circle Montessori
Arlington House Montessori
Children's House Montessori
Montessori Children's Center
McLean Montessori
Chesterbrook Montessori

and the Arlington Public Schools Montessori Program

There is also an Arlington Montessori Action Commitee, that I highly encourage you to seek out if you are serious about a Montessori education for your child.  www.arlingtonmontessori.org 
They have events and "going outs" and such.  They seem a little tied to the public school system, but in general, are a very good source of information.  You can get on their email listserve as well.