Awhile back, I posted this wonderful link that offers great audio, stunning video/animations to go with the music, and terrific analysis of all the fugues in both Well-Tempered Clavier books - and now I'll give you another.
Here's a site where you can download PDFs of both Well-Tempered Clavier books; each book comes in two parts (#1-12 in Part 1, and #13-24 in Part 2). All Preludes and all Fugues are included.
I've been meaning to go over to that other site, the one with audio and video, and thank that guy for doing all that incredible work - and I think I will....
(Yes, this is Chantblog, but for me J.S. Bach is a serious weakness. Indulge me.)