all the classroom in a book series are excellent, not cheap, but you will learn alot by sitting down and doing the projects step by step; another one just for inspiration with illy is "The Adobe Illustrator CS2 WOW! Book,". It has freebies included in the disc along with the files to take apart and explore, a really good resource and training tool.
A lot of it comes down to preference (flip through some books at the book store and see which ones look as if they might be useful to you) ... I generally prefer the visual quickstart books, but it's been a while since I've purchased any in that series.