The Lao nightlife is quiet and laid-back, usually involving a Beer Lao, a stunning sunset, firefly display and an early night. There is not much nightlife outside of Vientiane and Vang Vieng. To have a beer in some places, simply visit a restaurant.
Vientiane has a few bars/clubs, but there's no shortage of places for a quiet Beer Lao. In particular, the Mekong shoreline is packed with near-identical but pleasant bamboo-and-thatch beer gardens offering cold beer and spicy snacks.
At dusk, wander down to the riverside quay on Fa Ngum Road. The Lane Xang Sunset Cruise boards at 7 pm and includes meals from $8 and affordable drinks. Passage is free and the cruise lasts about an hour and a half.
Back on land, there are a few places to meet and greet. The Khop Chai Deu, on the southwest corner of the Nam Phu Fountain, is the hot spot for expats and travellers, and a good place to find out what's going on in town. For a more laid-back atmosphere, try Jazzy Brick, across from Khop Chai Deu, or the Chicago Bar, on Rue Nokeokoumane across from Wat Mixay. If dancing is your thing, check out Dtec Disco at the Novotel hotel. Note that everything is supposed to close down before midnight before the start of the unofficial curfew, although clubs generally stay open until 1-1.30 am. The most notable exception is the extremely popular Don Chan Palace Hotel Nightclub which is open until 4 am on the weekend.
For live music, try Chess Café, on Sakkaline Road, just off Fa Ngum Road east of town, or On the Rock, an intimate affair on the corner of Fa Ngum and Manthatulat Road.