Just to continue the shout outs for Josh Dever's excellent project of putting philosophy dissertations up online. I learned lots from reading dissertations when I was a graduate student (in particular, from John MacFarlane's and Cian Dorr's). The best dissertations not only give you not only a bunch of cutting-edge ideas, but also hugely useful surveys of the philosophical backdrop. They also give ideas of the "big picture" that's informing interesting people's work. I found them more interesting than most books (though I guess I was looking at a biased sample!)
A final thought. It's being suggested that online dissertations can be put in for the latest RAE exercise in the UK (any "public domain" paper is allowed to be put in, but obviously not too sensible to put in any old scrap: but dissertations that have gone through viva-ing are a natural candidate to be put in). Perhaps we'll see more dissertations going online because of this.