Even in the age of the Internet, the best resource I've ever found for information on comics is the Slings & Arrows Comic Guide. Originally published in 1997, a second edition came out in 2003. The great thing about the guide is that it's not a price guide like Overstreet; it's a compendium of reviews of pretty much every comic, mainstream and independent, published in the last several decades. Some of the reviews are quite thorough, spanning several pages, while others are just a few words like this description of Image's 1993 miniseries, The Pact: "Mindless violence between preposterously proportioned individuals." The guide has even expanded my language skills by introducing me to great British slang like "Kack" and "Bog Standard". If they come out with a third edition, I'll definitely grab it.