I too worked at Dulles Aviation in Manassas (summer/fall 2000). It's a busy school (I think I averaged about 120+ hrs a month during the summer). Tom is a tough boss, but they take care of their employees.
I would recommend against AVED in leesburg... I got burned by them after they offered me a job in April (To start in may) and then filled it without telling me before I moved across the country to start (resulting in me being not happy). In addition, I was much more impressed with DAIs fleet than AvEds (at least when I rented planes back around 1998).
As for Chantilly Air, I don't know what the deal there is... I know several people there (pilots that were former coworkers of mine) that are pretty happy flying for them. There are certainly a few things they wish were different (like the CP not taking all of the good trips), but overall I've heard nothing bad about the company.