Avenida de las Artes provides a comprehensive guide to the Santurce arts district, with a visual history of the neighborhood, suggested street-art routes, and schedules for performance venues.
Sal.pr, published by Puerto Rico's main newspaper, El Nuevo Día, is a comprehensive restaurant guide with user reviews.
To learn more about the island's unique bioluminescent bays, check out biobaypuertorico.com, which includes a useful moon calendar (nights with a bright moon should be avoided).
San Juan's small but vibrant alternative art scene is blogged about at length at Puerto Rico Indie.
Puerto Rico Day Trips will not be winning a web design award any time soon, but it provides useful information about everything from hidden beaches to street festivals