StackOverflow is an awesome source of information. I guess most will use it in “I have a problem – lets ask on SO – cool, I got answer, back to work” way.. But, this site has some very, very knowledgeable people answering there, and just going through their answers will bring up a wealth of information. I’ve went through Eric Lippert’s, almost done Jon Skeets, and have a few more lined up – and a) they’re very relevant to every C# developer (even if you don’t use them in your everyday work – knowing your language of choice really well is always a good thing) b) they’re covering areas I didn’t see covered in any book, because books tend to be pretty general by their nature.