Depending on your tastes, you could also check out 14th Street NW - U Street corridor, Adams Morgan, Barracks Row (Eastern Market) or the H Street NE - Atlas Arts District. Parking is often difficult, so probably best to park outside the District and use Metro or taxis to get around. The main streets in most neighborhoods are fairly safe at night but there can be problems if you venture off onto side streets where there is less foot traffic.
Some of the off-the-beaten path sites include: The National Building Museum; National Museum of Women in the Arts; the Phillips Collection; National Arboritum; Kenilworth Aquatic Gardens; Eastern Market Flea Market (Sundays).
Nightclubs: Twins Jazz; Lima; Josphine; 14th & Park (14th Street NW - U Street corridor); Rock and Roll Hotel, U Street Music Hall (H Street NE)
Restaurants and bars: Saint Ex, Rice (14th Street NW - U Street corridor); Dangerous Pies, Granville Moore's, Sticky Rice (H Street NE); Matchbox, Banana Cafe (Eastern Market)
Shops: Millenium Decorative Arts; Pulp; Miss Pixie's (14th Street NW - U Street corridor)
Art spaces: H Street Theater, Atlas Arts (H Street NE) Transformer, Studio Theater (U Street - 14th Street); The Fridge (Eastern Market)
Pick up a copy of the free weekly, Washington City Paper, when you get here for more details on events and nightlife. Also check out Brightest Young Things and DCist blogs for event calendars.