Robert Shea's novels are well worth reading and I encourage everyone to explore them.
If you prefer books on paper, you can order used copies of all of his titles, and Robert Shea's son Mike Shea also has made paper editions of some titles.
But if you are fine with ebooks, good news: Mike Shea has released all of the titles under the Creative Commons license. There are reasonably priced titles in the Kindle format on Amazon, but you can also get good editions for free. Here is my guide for getting good, free Robert Shea ebooks.
For my favorite, All Things Are Lights, get it on the Internet Archive, where you can download two convenient formats: mobi (for Kindles) and EPUB, usable on all other tablets and phones. I downloaded the mobi file and sent it to my Kindle and it worked fine.
You can also use the Internet archive to get copies, in the same two formats, of the two Saracen books, The Saracen: Land of the Infidel and its sequel, Saracen: The Holy War. (Really, they are one work, published in two parts.) The Internet Archive also has Shea's Native American historical novel, Shaman.
Project Gutenberg also has some Robert Shea titles at one convenient location, including Shaman and the two Saracen books.
Shike, available as an inexpensive Kindle ($2.99 for both volumes) also is available for free in HTML at bobshea.net. $3 is cheap enough that I just bought it, to have it for my Kindle. There were problems for awhile with the text of the Kindle edition, but Mike Shea tells me those problems have been fixed.
My next two posts for Robert Shea Week will be guest bloggers who will explain why you should read Shea.