Detexify: draw to find a LaTeX symbol
LaTeX has to many symbols that finding the right one is difficult. If you cannot put the symbol into words, you cannot Google for it. A while ago, I had an idea for quick lookup: record what typable character a symbol looks like and search for the symbol via the character. Recently, I've stumbled across a solution that is much neater than this: Detexify lets you draw something and then does a search for symbols that look similar. Cool and useful.