What are some good "under 21" nighttime activities in or around DC?

Answer 1

There's no "Under 21" dance clubs any more although a few clubs still let in the under-21 crowd.

9:30 Club (930.com, 8th and V NW) is a great live music venue; all ages, all the time. They are VERY aggressive about carding and enforcing no alcohol rules for folks under 21 so don't even try it unless you like getting kicked out. But you can see some amazing bands here. Sound system is fantastic. Sometimes you can go hang out in the "back bar" area which is downstairs without paying for the show but that all depends on who's playing. But if you're under 21 and want to see a band, that's where to go. They're not open unless there is a band playing.

Black Cat (blackcatdc.com, 14th and S NW) also has live bands but they're also open every night; you can go watch the bands if you want (pay for admission) or hang out in the "Red Room" bar area with no cover. There is a pool table and pinball in the Red Room.

Answer 2

Try warehouse next door http://www.warehousenextdoor.com/ also browsing on the DCinfoshops myspace http://myspace.com/dcinfoshop might help you keep your finger on the pulse.