The Annual Downtown "Holiday Market" in Chinatown is open through Dec 23rd from noon - 8:00 daily. Across from the Verizon Center metro exit and the American Art Museum and Portrait Gallery between 7th and 8th on F St, NW. Free to visit, but much more fun if you go to shop!
Ice Skating on the Mall at the National Gallery of Art Sculpture Garden! The rink is open 'til 9:00pm most nights and ‘til on Fridays and Saturdays! Cafe on site open 'til 7:00 most nights and 9:00 Friday and Saturday. Admission to the rink is $7.00. Open winter only, through March 9th.
The Insight Meditation Community of Washington offers a Buddhist based meditation class on Sunday eves from 6:00 - 7:30 at All Souls Unitarian Church in DC at 16th and Harvard and on Wednesday eves in MD at the River Rd Unitarian Church. If you are interested in learning meditation, this this a great group. Classes are free but donations are always appreciated.
Free concerts at the Library of Congress on Fridays nights! Tickets are required. Details in previous post, including a link to their calendar.
Free concerts at the National Gallery of Art every Sunday night at 6:30! World class performances for free. See their website for a complete calendar. Link in previous post.
Learn Qigong/ Tai Chi on Saturday mornings from 10:00 - 11:00 or Sunday evenings from 5:00 - 6:00. Donation based. Saturday morning class is led by Nate and Sunday eve is led by Ken, prior to the meditation class led by IMCW at All Souls Unitarian Church, 16th and Harvard. Note that the Saturday morning class will not be held during the summer months.
You can also see lots of great art as well so be sure to type in the keyword Art to see those. Open-mic and poetry events are also listed, even some comedy nights. Museums of note such as the DEA Museum and the Apothecary Museum are also little known attractions in the area. You can find half price tickets through TicketPlace as well and many theaters have pay-what-you-can deals for new shows prior to opening weekend. Of course, there are all of the Smithsonian Museums that you all know about as well, open daily and always free.