How to search for mathematical symbols in LaTeX

Detexify

The easiest way to search for a math symbol is Detexify. This webservices allows you to draw the symbol. It looks like this:

Symbol tables

Arrows

$\rightarrow$	\rightarrow	$\leftarrow$	\leftarrow	$\Rightarrow$	\Rightarrow	$\Leftarrow$	\Leftarrow
$\leftrightarrow$	\leftrightarrow	$\Leftrightarrow$	\Leftrightarrow	$\nRightarrow$	\nRightarrow	$\nrightarrow$	\nrightarrow
$\leadsto$	\leadsto	$\mapsto$	\mapsto	.	.	.	.

Greek

$\alpha$	\alpha	$\beta$	\beta	$\gamma$	\gamma	$\delta$	\delta
$\zeta$	\zeta	$\eta$	\eta	$\theta$	\theta	$\epsilon, \varepsilon$	\epsilon, \varepsilon
$\iota$	\iota	$\kappa$	\kappa	$\lambda$	\lambda	$\mu$	\mu
$\nu$	\nu	$\xi$	\xi	o	o	$\pi$	\pi
$\rho$	\rho	$\sigma$	\sigma	$\tau$	\tau	$\upsilon$	\upsilon
$\phi$	\phi	$\chi$	\chi	$\psi$	\psi	$\omega, \Omega$	\omega, \Omega
$\Phi$	\Phi	$\varphi$	\varphi	.	.	.	.
$\Lambda$	\Lambda	$\Delta$	\Delta	.	.	.	.

Operations

$\cdot$	\cdot	$\oplus$	\oplus	$\times$	\times	$\nabla$	\nabla
$\pm$	\pm	$\mp$	\mp	$\cup$	\cup	$\cap$	\cap

Relations

$\approx$

\approx

$\sim$

\sim

$\cong$

\cong

$\neq$

\neq

Calligraphic Letters

$\cal{O}$

\cal{O}

$\mathfrak{M}$

\mathfrak{O}

$\mathfrak{R}$

\mathfrak{R}

Sets

$\mathbb{N}$	\mathbb{N}	$\mathbb{Z}$	\mathbb{Z}	$\mathbb{R}$	\mathbb{R}	$\mathbb{C}$	\mathbb{C}
$\mathbb{A}$	\mathbb{A}	$\cap$	\cap	$\cup$	\cup	$\in$	\in
$\subseteq$	\subseteq	$\subsetneq$	\subsetneq	$\notin$	\notin	$\bigcup$	\bigcup

Other

You might need \qed, \qedsymbol, \blacksquare for proofs. It is the Tombstone $\blacksquare$

I've recently needed $\dots, \ddots, \vdots$ (\dots, \ddots, \vdots) for a visualization in a matrix. Note that you can write ... instead of \dots, but you'll lose the semantics.