As a general rule, particularly in the sciences, the best people to ask for recommendations for books are second year graduate students in the field.

You really get to know how well you learned something when you need to use it; for example, in a class for which it is a prerequisite, and you get to know which references are the best when you need them. In the first few years of graduate school, you end up in classes with other students from a variety of different schools, who used a variety of different textbooks for the material needed for the undergraduate degree. Unless the students in a given department are particularly antisocial, after a year of classes together the group will have learned which undergrad textbooks are the most useful.

Yes, this applies even to introductory level textbooks.

It's out of date now, but when it was current Frank Shu's The Physical Universe was as good as I could find.

If there is a particular field you want to get "up to date" in, the Annual Review for astronomy and astrophysics is a great resource, but something you are likely to need a good library for.