Books that go beyond plain calculus; and some thoughts about books
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After you've done calculus, if you want to go further, the following
are the best available books on the next 3 subjects:
  E.L.Ince: Ordinary differential equations (Dover).
  R.Horn & C.Johnson: Matrix analysis (Cambridge Univ. press).
  G.Golub and C.Van Loan: Matrix computations (Johns Hopkins
  Univ. Press).
  R.Remmert: Theory of complex functions (Springer).
Note, these are too much for undergraduates (or even
most pros) to digest in one gulp, but that does not matter -
they deliver tons of good useful stuff in a form useful
as a reference. Do not fall into the TRAP of thinking "I want
the `easy' book designed for dummies."  Often, really, the
best books for dummies are the same as the best books for experts,
i.e. the best books, full stop.  Books covering more stuff can be better, not
worse, especially if it is all independently accessible without
reading though everything else first. Another TRAP is to believe the 
newest book is the best.  That can be true in rapidly changing areas 
where stuff quickly gets out of date, but, in well-established areas 
of math - i.e. most low-year undergraduate courses - older books can
be just as good or better, and papers written in 1900 can remain 
fully as good today!
A final TRAP is to believe courses & books involving computers are
better than those without.  That can be true - and in the modern world it
is essential for any scientist or engineer to be able to program -
but often it is best for you, the human, to be the center of
attention.  It's about thinking.  Once you the human understand
something, often computerizing it will be no problem.