Rparz,
There are a lot of great books out there. Linnerts Welding Metallurgy was one of my first. The ASM (especially Volumes 4, 6, 8, and 10) and AWS Handbook series'. IIW has a tremendous library of tech articles(free). Lincoln, Miller, Alcotec, and Nidi, have terrific websites with articles(free). ESAB has some very good Handbooks. The Welding Journal Research supplement. TWI, WRC, the Department of Energy, Woodhead Publishing are other great resources. ASTM has some great technical publications. And once you start collecting these they will of course reference others and the snowball grows. Before too long your wife is complaining about why you haul this tonnage around with you wherever you go.
But to be honest, the greatest resource of information that I've been exposed to is people. People in AWS, ASME, ASNT, EPRI, TPA, etc. There are a lot of great people out there that are more than willing to share their knowledge (like many in here) with others who demonstrate a desire to apply themselves.