A useful resource I'm still looking into for my work purposes - but would also be useful for any budding MMOG developers (Or just general coders/techies) is Safari. It is, basically, an online library of almost 2000 books from various publishers. You can sign up for a 2-week free trial here, and there's varying pricing afterwards depending on how many books you want to 'check out' at a time - I believe its $9.95 for a 5 'point' subscription per month (Most books are 1 point, some are less, some are more).
I'm currently reading Designing Virtual Worlds by Dr. Richard Bartle, who most of you will know as the co-creator of the original MUD - it's an interesting book so far - certainly eye-opening in some regards!
They have a BUNCH of books there so certainly worth looking into - it was VERY helpful when I was looking for some information for work!