As part of Barack Obama's Day of Service on Martin Luther King Day, there's a Kenyon Street clean-up from 10 am to noon on the 19th. The group will meet at 650 Kenyon Street NW and make their way west to 14th, and if there's a big crowd, expand to other streets too.
So sign up, and dress warmly! The cleaner-uppers are meeting at Wonderland after they're done.
And if you want to do more (or don't want to clean up streets but still want to help) there's a ton of other events too.