Books that I find very good, interesting or relevant (in particular I like books from a geometric point of view):
Topology by James R. Munkres
Algebraic Topology by Allen Hatcher
An Introduction to Manifolds by Loring W. Tu
Differential Geometry: Connections, Curvature and Characteristic Classes by Loring W. Tu
Gravitational Curvature: An Introduction to Einstein's Theory by Theodore Frankel
An Introduction to Theoretical Fluid Mechanics by Stephen Childress
A Course in Complex Analysis and Riemann Surfaces by Wilhelm Schlag
Mathematical Methods of Classical Mechanics by V.I. ArnoldÂ
The Mathematical Theory of Finite Element Methods by Susanne Brenner and Ridgway Scott
Lectures on Discrete Geometry by Jiri Matousek