Tales of the Jedi Companion will probablly be the most important, and hardest to find, book. that online auction site had them for ~ $35 last time I looked, and that was over a year ago. Still, it works out to being cheaper than buying WotC d20 books. Fragments from the Rim isn't bad. Cracken's Field Guide is good. Tramp Freighters, Pirates&Privateers, and Stock Ships are all good to have if you're dealing with ships & customizing them. the Fantastic Technology books are good, esp "Personal Equipment" Lords of the Expanse & Player's Guide to Tapani are essential if you're doing a noble houses/intrigue/political campaign, but otherwise are just cool info. Heroes & Rogues is a great book for character templates. Instant Adventures are good. The other books are important only if you need that type of info. If you aren't going to have Yavin or Bespin based adventures, the Yavin&Bespin book probablly isn't worth investing in.