DC Native here...
The newest places are as follows:
Town- A huge two-level dance club... new york style hugeness. Friday nights are younger guys... Saturday nights is a more eclectic crowd.... young to older. Its a great great club and its a TON of fun if you want to dance. (Located at 8th and U St. NW, Washington.... don't walk around if you dont know the area, its not DANGEROUS but its not the BEST neighborhood either. Just cab it from door to door.) Make sure to bring cash, because the bar only take cash.... but there is an ATM inside just in case.
Nellies: 9th and U St, NW. A bi-level sports bar. Popular with people in their mid 20s to 30's. Really fun to hang out and chat it up with friends. My personal favorite overall... unless I'm in a dancing mood, in which case I'll head to town, which is literally a block away.
Halo: 15th and P st, NW. (Across from the Whole Foods). A more classy joint... usually a working professional sort of crowd. Its the place to see and be seen. Be prepared to look pretty and find people who think they are the sh*t standing around. its a little pretentious but its a nice bar, great ambience/lighting and the drinks are yummy too.
Cobalt: Used to be the center of gay life (was my favorite), but it sort of died off when Town opened up.... 17th and R St, NW. Still popular on thursday nights with their famous Underwear Contests.... lol.
Apex: Used to be the big dance club, but also kind of died down when Town opened up.... I've heard the crowd is 'interesting' nowadays...
JR's: 17th & Corcoran, NW. A fun bar with a wide range of people. Slightly older crowd. Fun 'theme' nights throughout the week.
Yeah, I think thats about it... I'm trying to think if there are any other places.... those are the most popular ones... message me if you like / have more questions!