There are several bars clustered around José de la Mar and Cajamarca to still your thirst.
El Tambo, 2 blocks from Plaza Ginebra. Popular weekend club (slow on Thursday) that plays mostly salsa with short sets of house, reggaeton, and American music. It has a tree / wood theme.
Cafe Andino, 2 blocks from the Plaza de Armas, closed Mondays and January/ February. Delicious espresso and other coffee beverages. Can buy beans too. Excellent selection of books to borrow (with deposit), and good magazine selection to peruse while there. Loud, familiar music (Marley, Grateful Dead...). Friendly, accommodating staff. Great atmosphere. Free WiFi. Expensive, but good and healthy gringo food.
California Café, Jr. 28 de Julio, 568. Café with a big book exchange, also doubles as library. The Californian owner organizes ultimate frisbee matches every Friday. Just drop in at around 130PM (Dry Season, April-November) or 10AM (Rainy Season, December-March) if you're interested. One of the house specialties is their mixed fruit smoothie, called Surtido. This cafe also serves roasts its own coffees and is an ideal spot to hang for a few hours when first getting into town. Try their sandwiches, made to order with lots of variety. Also has free WiFi.
13 Buhos BarJose de la Mar & Simon BolivarThe owner, Lucho (who bears an uncanny resemblance to George Clooney), brews handcrafted ales, although he can be a bit pushy in trying to get customers to buy drinks. Typically there are a few varieties on offer: a dark hoppy stout or porter, a red, and a fresh lager that when muddled with yerba buena is delicious. Reviews are mixed: some people love this place, others swear that it should be avoided.