We live in Vienna and take our 2 and 3 year old children to Community Montessori School in nearby Reston. (It's only 11-12 minutes from our house) Our next-door neighbor's children also go there.
It's a very good school with well-trained, caring teachers. Very clean - the kids have had a lot fewer colds and illnesses than at their old school. They follow Montessori teaching practices, but aren't fanatical about it so they are able to be a little flexible according to each child's needs.
They also have very flexible schedules available - just mornings, all day, a few days per week, etc. Our kids used to go every day until 6:30, but since I quit my job to start my own company they only go until 3:30. Some kids only go a couple of days per week; some only go until noon. Few other local schools offer these options.
The rates are posted on the school's website at www.communitymontessorischool.com. The pricing depends on your schedule. Most of the good schools/day cares in the area are about $15-18K/year.