I used to pay attention to the radio or mainstream news rags like Rolling Stone. Free local weeklies are a great source of live music schedules, but not consistently reliable when reviewing recordings.
Friends are the bulk of the grapevine.
Friends whose musical tastes may differ, but their willingness to share with an open mind doesn't. Friends who take you on long late night drives when you come to town so you can play new albums for each other. But another important source is record labels. No, they're not. There are many labels out there who do a good job of supporting their artists and providing wonderful new music for the listener.