I wish I had read this thread earlier. I just checked at RPGNow (my primary source), and they have me as buying 311 pdf's since 2002 -- that's almost entirely d20 material. If you count in some of the other places I have purchased from (White Wolf, DriveThruRPG now that they have partly rid themselves of that DRM thing) and free stuff/web support from Wizards and others, I probably have well over twice that number, say 700+.
Some of my favorite stuff comes from:
Malhavoc Press -- I own everything they have published on PDF, with the exception of the psionics books, since I don't use psionics in my campaign. I would give my eye teeth to know what well Monte Cook and Co. go to for their ideas.
E.N. Publishing -- Well done, good ideas, stuff that's all over the map.
Ronin Arts -- Phil Reed really believes in the PDF form for game publishing, and he seems to have made the "PDF publishing for short ideas" paradigm work as well. I know I have a number of his different lines of product.
RPGObjects -- I absolutely love their Darwin's World post-apocalyptic game (d20 Modern).
0One Games -- They are looking to use the capabilities of the PDF format to their advantage; their map product lines are incredible.
I love PDF for a number of reasons -- 1) Space: I belong to a family of readers, and we own so many physical books that shelf space is at a premium in the house. PDF allows me to get around that. 2) Price: Most PDF's, if available in both hard and electronic copy, cost about half what the book would be. True, it's more if you want to print a hard copy, but that leads to another point: you print what you want or need, and leave the rest on disk. 3) Portability: Want to bring material to your next game? Would you rather hire a pack horse or grab a fistful of disks? 4) It allows someone with really cool ideas but without either the means to get them to print or the length necessary to justify a print run to publish those ideas anyway (Phil Reed is a prime example here).
There are limits to PDF usability -- with especially large texts, particularly if you plan to print them out, you're just as well off money-wise buying the hard copy -- but in my mind, these are far outweighed by the advantages.
