Pros
Great location - in the center of DC, in a great building with a food court, within walking distance from the National Mall and all major monuments.
The company has competitive pay and benefits (and new very liberal paternal policy!) and is overall a great place to work at. Very diverse, a lot of interesting folks committed to international development.
Flexible working hours and options to telecommute. I particularly appreciate the flexibility and attention to life-work balance. I mentioned open office space as a con, but it also has its positive sides - you see your colleagues and have more opportunity to engage with them and the senior leadership, which is not just honed inside their offices. Also, because of telecommuting options, one can always work from home when needed.
Cons
The only con is the office space - an open floor plan. There are no offices, no cubicles. The meeting and huddle rooms book up quickly. Making calls from your desk is problematic as there is always someone who will try to "hush" you. Sometimes makes it difficult to work on tasks that require concentration.
The number of paid vacation days could be better.
