I think it’s immensely helpful to gather up “road maps” of different math subjects. (See Ideas to implement.) Here are lists of math book recommendations on the web.
What would be really useful for me is a road map for each math subject, and a list of book reviews gets us halfway there. Firstly, each subject consists of many topics, and different books cover some topics but not others; second, there may be various ways of viewing the subject and deriving the theorems, and it’s good to list out which books take which kind of approach; third, some books are better for learning and some better for reference. Finally, I think in this age such a list no longer has to be constrained to print books; there are more and more electronic resources available for all the subjects. With technology I feel learning now has more of a “scavenging” component – sometimes a blog post, or a student’s thesis, for instance, can be very useful.