My blog has a link to a free sample chapter on Generics. As this is one of the more confusing subjects I thought I would let people know about it. It is a sample chpter from the Learning Java book from OReilly.
I am using the SCJP Sun Certified Programmer for Java 5 Study Guide book as well but I find sometimes it is useful to read about a subject from a different writer
Here is a link to the blog entry, it does have other SCJP stuff as well
As free chapters go it's a pretty good one. It's a weighty 36 pages long and goes into a decent amount of detail. Most importantly it's free
I think one of the main hurdles when trying to learn generics is seeing Generic code. I found it quite different from normal Java code. So I found that reading generic code helps understand, especially when you see it and understand what they are trying to achieve.