Andrea Ferretti has just revealed his new project: MathOnline is a searchable catalog of free online mathematical references. For example, here are all the online guides to Algebraic Number Theory. The focus is on expositions, not research (we already have the arXiv), and all material should be legal for redistribution. There is clearly a lot of work to be done filling in the catalog, but I think this site could become really useful. Head over there and add your favorite texts!