Bill Trench pointed out this web site (Digital Commons Network) committed to organizing open-access publications and this sub site dedicated to mathematics.
If you are not familiar with it, the open-access movement is a recent development that is a response to the barrier presented by commercial publishers (particularly commercial journals) to easy access to scholarly work. You can read more about this movement at the Open Access Pledge site (I haven't made the pledge yet, but I'm busy right now typing this post.)
While the focus here is on scholarly research papers and assuring that they reach the public in a timely fashion, until Bill pointed it out, it didn't occur to me that open-source texts would be candidates for open-access archives. Bill's recently open-sourced texts can be found on the Digital Commons site. If your open-source text is not there, I encourage you to get it placed there.