Two Websites for you to have a look at which might help you with concerts
etc.

www.wgms.com is the local classical music radio station and has an 'Arts in
Washington' section as well as ticket links

www.kennedy-center.org (I think that's the correct URL from memory -- if it
doesn't work try as search engine for the Kennedy Center) has a complete
calendar for everything at the Center.  Also -- there is a free concert
there every weeknight at 6pm on the Millenium Stage in the main foyer --
content and artists vary every day.

Tim
Alexandria, VA