If you wanted to insert some symbol in a word processing application, you’d probably open up a character palette or symbol map, and browse through various fonts (wingdings, dingbats…) to find that elusive symbol.
In LaTeX, the Comprehensive LaTeX Symbol List has just about every symbol imaginable in LaTeX, from mathematical operators and symbols (including Greek letters), the Euro symbol, wingdings, dingbats, blah blah blah. The list is accessible as a PDF on your local installation via the commands texdoc comprehensive on TeXLive, or mthelp –view comprehensive on MikTeX.
However, browsing through the list is still rather tedious, even if the document has a good index to make searching a leeeeeetle bit easier. Detexify is a free online tool that greatly simplifies the hunt for a LaTeX symbols. You sketch your symbol with the mouse, and detexify tries to classify it and returns the appropriate LaTeX package and command required for rendering it.
Here’s an example of a “null” symbol. The 2nd symbol in the list is the one I’m looking for, so I’m going to include the lines
\usepackage{amssymb} … $… \varnothing … $
in my .tex file.
Here’s another example of a maths symbol.
Wingdings and dingbats work, too. In fact, I haven’t even finished drawing the envelope, and detexify has already showed me \Letter from the marvosym package.
Awesome!