Well there are 2 main beers: 'Cristal' which is light and easy drinking, and 'Bucaneer' which is a bit stronger. Both are good but you'll only find them in bottles (Which is good cos it's cold longer!).
As far as bars go, La Bodeguita del Medio is essential just cos it's so small and cool but the mojito is disappointing, equally disappointing everywhere else as well mind you. The other essential is La Floridita (Hemingway's other haunt), ask for a Hemingway daiquiri and you'll get the best drink in town.