The blog post at www.querytracker.blogspot.com is a great one. It features an interview with Steve Weber who wrote Plug Your Book! Online Book Marketing for Authors. Its really a great interview. He sings the praises of networking sites and I am quickly turning in to a believer.
And what do I have to say about Twitter, now that I've bit the bullet and joined? Cooool. Twitter, where have you been all my life?!?