1) The Knitting Stitch Bible
2) The Knitters Book of Finishing Techniques
3) Big Book of Knitting
4) The Knitter's Companion
I own hundreds of books, and love them all, but these are 4 books that are very useful for different reasons.
If you can ever afford to spend money on classes...save the money, don't take an expensive class. Use your education budget and purchase the Knitting Daily TV
DVD set. Each 4-disc DVD set has 5hrs/48min of instruction. Holy cow. I've learned so much my head nearly bursts. Simple, useful, ingenious stuff. I've also learned things about stuff I'd never dream existed.
They can be purchased here.
I personally own Series 100-800. (all of them) They are all wonderful, and worth E.V.E.R.Y P.E.N.N.Y!