Utility Websites
These websites offer powerful tools.

Detexify. Search for Latex commands by handwriting symbols. The description of the command includes the package (if nonvanilla) and whether it should be used in math mode or text mode.

When2Meet. Find overlapping scheduling times. One person must create the poll at the provided link by choosing the dates (by default, the time windows are set from 95, but this may also be changed.) Once made, a link to the poll is created. Here is an example poll, where I have indiciated one person to be available on MWF from 1012AM and TR from 13PM. As more people fill out the poll, the schedule on the left will change; the brightest green indicates where the overlap occurs, and the more faded sections indicate less overlap. White indicates no overlap.
Software
These programs range from quite useful to absolutely essential, with a focus on open source or freely available software.

LaTeX. LaTeX is the sine qua non in document creation and academic publications. The easiest way to use the software is to obtain one of the recommended distributions on the site, together with an editor such as Texmaker.

SumatraPDF. A lightweight, open source document viewer for Windows that notably also supports many other document types such as
.djvu
files in addition to the standard.pdf
. 
Foxit Reader. Foxit is a proprietary company, but their document reader (as opposed to editor) is available for free. Notably, their free reader contains document signing capabilities, which Adobe’s does not allow.
References
These materials, be they in digital or print, are useful sources of mathematics, physics, pedagogy, and other topics.
Mathematics
Subject  Author  Title  Publisher/Series  Notes 

Complex Analysis  Lars V. Ahlfors  Complex Analysis  MacGraw Hill  A wellregarded introduction to complex analysis with good geometric treatment of the subject. 
Wilhelm Schlag  A Course in Complex Analysis and Riemann Surfaces  AMS Graduate Studies in Mathematics  
Wolfgang Ebeling  Functions of Several Complex Variables and Their Singularities  AMS Graduate Studies in Mathematics  An analytic take on several complex variable theory.  
R. Gunning & H. Rossi  Analytic Functions of Several Complex Variables  Prentice Hall  A more cohomological take on several complex variable theory. 
Teaching
 Apex Calculus. An open source calculus textbook. The
.pdf
version is free to download, and print copies may be obtained for a low cost. Many UCR calculus courses use this book.