Ultimate Reference for Symbols

While not the easiest to search, this reference contains a list of every LaTeX symbol you could ever want, as well as a lot of other advanced information about LaTeX characters and processing. It's a delightful resource put together by Scott Pakin in 2003, but it's held up well. I keep an archived copy for my purposes:

I have also archived a publication containing a slightly more abridged collection of math symbols and tutorials from AMS:

Revision #2
Created Sat, Feb 1, 2020 6:07 AM by Garrett Mills
Updated Sat, Feb 1, 2020 6:13 AM by Garrett Mills