The CBO has for the past 40 years provided specialist advice to Congress. It is an institution well worth looking at and getting to know if the workings of Congress itself are of interest to you.
Brookings have an event next week - which I've already signed up for - not that I will be in Washington (more's the pity) - but one can sign up for the live webcast.
For more details - and to sign up (either to attend in person, or for the webcast - go to http://www.brookings.edu/events