While the NBER continues its rather ridiculous policy of gating access to NBER Working Papers – they are nearly all available freely after a quick search on Google Scholar, so why not just make the link in my NBER New Papers emails go to a pdf I can read? – Yale’s wonderful Cowles Foundation has taken a great step in the opposite direction and made a huge number of their classic papers and monographs freely available online. A few of the books you might be particularly interested in if you like the regular content on this site are Marschak and Radner’s legendary work on team incentives and the internal organization of firms, and Debreu’s Theory of Value (which still might be suitable as a textbook on general equilibrium analysis).
The full collection of Cowles’ work online can be found here.
A Fine Theorem 
The NBER must be violating some NSF rule with the closed access policy.
If only there were such a rule! The NIH has an open access (with delay) rule. The NSF is considering a similar rule, but actually, a handful of imbecile congressmen currently have a bill called the Fair Copyright in Research Works Act would reverse the NIH policy and ban other government agencies like NSF from setting up similar rules. It’s madness. I have a paper in progress currently that tries to tease out whether open access policies “matter” and rough draft is that they do indeed.