Around the site there are a lot of questions about closed form expressions or approximations for specific series, products, limits and whatnot. These however are hard to find to the difficulty in searching for specific formulas.
Is there some resource online with a discretely comprehensive list of formulas, with proofs of the results, and organized in such a way to be easily accessible?
I guess the closest you come is with the NIST digital library of mathematical functions: http://dlmf.nist.gov/ which is destined to eventually replace the classic Abramowitz & Stegun: "Handbook of Mathematical Functions: with Formulas, Graphs, and Mathematical Tables (Dover Books on Mathematics)".
If google could only make a specialized search engine for mathematical expressions ...