I have a great condo townhouse for rent in the Brambleton (Ashburn). It is only three years old, 3BR/2.5 Baths and has a 1 car garage. It is listed for $2200 per month. Please let me know if you would like to see it. For more info click: http://washingtondc.craigslist.org/nva/reb/2727137490.html
Joe gave a great overview of the rental market in the area you're looking in. As you can see, there is not much available and when there is, it goes quickly.
I suggest interviewing a few agents to see which one would serve you and your needs best. Feel free to give me a call to discuss the available rentals near Mill Run Elementary, the rental market in general and see if we would be a good fit for each other as agent/client.
Below is a link for 2 townhomes for rent in Broadlands South. What price range are you looking to stay within? What is your timeframe? Rentals are going really fast and have been for some time. The average days on market for a rental near Mill Run is 14 days and both of the listings below have been on the market for 7 days already. In fact, the rentals in the 20148 zip code average 20 days on market over the past 4 months. Please give me a buzz or email me to see the listings. Myself or someone from my team could show you today.