Well, if you really want to read them Diane Duane is currently having a sale at her store. Here's her website with the info up top as long as it's going on. I do recommend getting the New Millennium editions if possible as they are the ones that have been edited to be less dated and establish the new official timeline. The books started in the 1983 and every subsequent book was set in the year it was publish, which has caused some interesting issues that Ms. Duane has set about fixing.

They are brilliant books. I highly recommend them to just about anybody.