Here I list some of the resources that might be of interest to some people in math. I have not created any of them! I have enjoyed reading, watching, and knowing about them and I just feel like it would not be a bad idea to help other see these works as well.
MacTutor Index - MacTutor History of Mathematics: MacTutor is a free online resource containing biographies of more than 3200 mathematicians and over 2000 essays and other supporting materials.
Home - Mathematics LibreTexts: This Living Library is a principal hub of the LibreTexts project, which is a multi-institutional collaborative venture to develop the next generation of open-access texts to improve postsecondary education at all levels of higher learning.
CURM: Center for Undergraduate Research in Mathematics Minigrants.
Here, I introduce some nice books that are both in my research interests and general interests in mathematics. You may find them useful for your own study/research. I have tried my best to mention books that I have either studied (fully/partially) or have had enough familiarity with their contexts.
Complex Analysis
Complex Analysis, An Introduction to the Theory of Analytic Functions of One Complex Variable, Lars V. Ahlfors, 1979.
Functions of One Complex Variable I, John B. Conway, 1995.
Basic Complex Analysis, Jerrold E. Marsden, 1998.
Complex Functions, An Analytic and Geometric Viewpoint, G. A. Jones, D. Singerman, 1987.
Classical Topics in Complex Function Theory, Reinhold Remmert, Springer-Verlag, 1997.
Elementary Theory of Analytic Functions of One or Several Complex Variables (Dover Books on Mathematics) by Henri Cartan.
An introduction to the theory of the Riemann Zeta-function, S. J. Patterson, Cambridge studies in advanced mathematics, no 14, Cambridge University Press, 1988.
Lectures on Complex Approximation theory, D. Gaier, Translated by R. McLaughlin, Birkhäuser, 1985.
Approximation of Functions, G. G. Lorentz, Chelsea Publishing Company, New York, 2nd Ed, 1986.
Riemann Surfaces, L. V. Ahlfors and L. Sario, 1960.
Riemann Surfaces, Farkas, H. M., Kra, I. 1980.
Lectures on Riemann Surfaces, Otto. Forster, 1981.
Geometric Function Theory and Conformal Mappings
Conformal Invariants, Topics in Geometric Function Theory, Lars V. Ahlfors, 1973.
Boundary Behaviour of Conformal Maps, Ch. Pommerenke, 1992.
Geometric Theory of Functions of a Complex Variable, G. M. Goluzin, 1969.
Conformal Mappings, Zeev Nehari, 1952.
Univalent Functions and Teichmuller Theory, Olli. Lehto, 1986.
Univalent Functions, Peter. L. Duren, 1983.
Univalent Functions, with a Chapter on Quadratic Differentials, Christian Pommerenke and Gerd Jensen, 1974.
Univalent Functions, Vol I and II, A. W. Goodman, 1983.
Principle of Mathematical Analysis, W. Rudin, 1964.
Modern Mathematical Analysis, M. H. Protter C. B. Morrey, 1964.
Real Analysis, H. L. Royden, 1988.
Understanding Analysis, Stephen Abbot, 2nd Ed, Springer New York, NY.
Invitation to Classical Analysis (Pure and Applied Undergraduate Texts), Peter Duren, 2012.
The Logarithmic Integral. Koosis P., Cambridge University Press; 1988.
Harmonic Mappings in the Plane (Cambridge Tracts in Mathematics, Series Number 156), Peter Duren, Cambridge University Press, 2004.
Mathematics of the 19th Century: Geometry, Analytic Function Theory, by Andrei N. Kolmogorov, Adolf-Andrei P. Yushkevich, 1996.
There's Something About Gödel: The Complete Guide to the Incompleteness Theorem, Francesco Berto, John Wiley & Sons, 2011.
The Way I Remember it, Walter Rudin, 1996.
A Mathematician's Apology, G. H. Hardy, 1940.
The Scottish Book, R. Daniel Mauldin, 2nd Ed, 2015.
Uncle Petros and Goldbach's Conjecture: A Novel of Mathematical Obsession, Apostolos Doxiadis, 2001.
Letters to a Young Mathematician, Lan Stewart, 2006.
Birth of a Theorem, Cédric Villani, 2011.
Gödel's Theorem: An Incomplete Guide to Its Use and Abuse. Torkel Franzén, 2005.