There's already so much stuff by Proudhon, Warren, Spooner, etc., that's already online, that just downloading it and reformatting it will keep me pretty busy. In the last couple of weeks, I've reformatted the online chapters (5 and 6) of Martin's Men Against the State that are up at The Memory Hole (the main work was keying in footnotes to ch. 5), and put together a pretty good pdf of Godwin's Enquiry Concerning Political Justice with a new pagination and table of contents. Just finding out what all's hidden away in the nooks and crannies of Project Gutenberg, Questia, and the Anarchist Archives could eat up a lot of time.
But as much as there already is, there's plenty of centrally important texts that don't (as far as I know) exist in digitized form. Some of the most important would be English translations of Proudhon's The Federative Principle and General Idea of the Revolution, and J.K. Ingalls' land reform stuff. And anything by Ezra Heywood. I've got an etext of the first half of Andrews' Science of Society, and jpeg images of the pages of the second half (both thanks to Joe Kelley), but no digitized version of the second half. Of course, that's just some of the biggest stuff, thrown out as an example of how big the gaps are.
So (I'm sure you saw it coming) here's the pitch. A project like this will require a distributed scanning network to fill in some of those gaps. I don't have a scanner, myself, although I'll probably be in the market for one in the next few months. In the meantime, I'm more than willing to put in the sweat equity editing the raw files from anyone else's scanning efforts. Shawn Wilbur is already doing a lot of scanning from the money writings of Greene, Kellogg, and Westrup. He's also interested in eventually getting as much as possible digitized from the entire runs of Liberty and The Word, probably the two most important periodicals to nineteenth century Boston anarchism.
I'm also curious as to just how much important material is already digitized and just sitting around on people's hard drives, but not available online. There are quite a few good scholars of the history of individualist anarchism out there, who are probably sitting on some really good stuff. If you're one of them, please, please, please--just click "attach" and "send"! Any contributions will be greatly appreciated.