This forum really is awesome.
My only problem is that I'm trying to cement my knowledge of all these number property rules and common questions etc., and these posts seem to be interspersed among all the other topics.
I have the MGMAT number properties
. It is excellent. Get the MGMAT word problems as well. It covers rates, work problems, combinatorics, probability etc.
Here's the catch, those two books are a bit rudimentary compared with the material on this website. But they are the only well written books that systematically and categorically archives all of the information. Start with those books, practice the theories with their questions, then apply it to the questions here.
If you ever find something here that has a comprehensive collection, let me know, I'd like to take a look, otherwise, sift and collect here.