I've bought more than 100 RPG books and accessories as PDFs, and never been disappointed with them. They have a huge catalog of obscure and out-of-print titles, including most of the classics from the early era of roleplaying in the 1970s and early 1980s. They also carry an incredible array of new games and supplements from small, independent publishers, including some really great games that aren't available anywhere else. If you're willing to read a game book on a tablet, print your own copy, or take the PDF to Staples to be printed out and bound, you couldn't find a better source.

Included among their offerings are literally thousands of free games and supplements. Some of them are amateurish efforts by first-time writer-publishers, but many of them are excellent, professional products offered for free as an introduction to a larger line. The free version of Stars Without Number, by Kevin Crawford, for example, is a complete SF RPG built on the d20 (D&D) system; download it to get an idea of the kind of excellent products you can find on DTRPG without spending a nickel. If you're only ordering free products, DTRPG won't even ask for a credit card--you just need a valid email to set up an account.

They also offer print-on-demand service for a significant portion of their catalog. I've only ordered one physical book from DTRPG, but it was well-made and delivered within the expected window (I believe about two weeks from placing the order to receiving the book). Although there are a small handful of negative reviews on this site about DTRPG's print-on-demand service, I've never personally heard of anyone having a problem that wasn't quickly resolved, and many of my friends (local and online) have ordered books from them. By the way, the printed book I ordered also included the PDF for free immediate download, so I didn't have to wait for the book to arrive to begin reading. Not every publisher listing their products through DTRPG includes the PDF with the physical book, but many do, so be sure to check.