Damn you mentioned pretty much the only pre-PT books I can think of. If you’re willing to go into the PT era, Darth Plagueis, Labyrinth of Evil, and the ROTS novelization are three of the best SW books I’ve read.
If we’re talking comics, the original Marvel run is an absolute delight. And the Goodwin/Williamson comics are fantastic, in both news strip and Classic Star Wars form.
As for purchasing, Amazon and ebay are both places you can find used books for dirt cheap. That’s where I get most of mine.
I have a question, are the Lando books any good?