Try this link: [link|http://wiki.cs.uiuc.edu/VisualWorks/Joy+of+Smalltalk|http://wiki.cs.uiuc...of+Smalltalk]
I don't know if it's the best book, but it's online and it's free. I actually liked it.
But, when you want to wrap your mind around the relationship between Class and Object and Metaclass and Behavior.... You are on your own. Wrack your brain til you get it.