here are some of my favorites.

\(\displaystyle \begin{array}{cc}

\backslash\text{pi} & \pi \\

\backslash\text{phi} & \phi \\

\backslash\text{equiv} & \equiv \\

\backslash\text{approx} & \approx \\

\backslash\text{perp} & \perp \\

\backslash\text{parallel} & \parallel \\

\backslash\text{cdots} & \cdots \\

\backslash\text{vdots} & \vdots \\

\backslash\text{circ} & \circ \\

\backslash\text{bullet} & \bullet \end{array}\)\(\displaystyle \begin{array}{cc}

\backslash\text{emptyset} & \emptyset \\

\backslash\text{cup} & \cup \\

\backslash\text{cap} & \cap \\

\backslash\text{subset} & \subset \\

\backslash\text{supset} & \supset \\

\backslash\text{vee} & \vee \\

\backslash\text{wedge} & \wedge \\

\backslash\text{flat} & \flat \\

\backslash\text{sharp} & \sharp \\

\backslash\text{natural} & \natural \end{array}\)\(\displaystyle \begin{array}{cc}

\backslash\tex{langle} & \langle \\

\backslash\text{rangle} & \rangle \\

\backslash\text{in} & \in \\

\backslash\text{sim} & \sim \\

\backslash\text{to} & \to \\

\backslash\text{boxdot} & \boxdot \\

\backslash\text{uparrow} & \uparrow \\

\backslash\text{rightarrow} & \rightarrow \\

\backslash\text{downarrow} & \downarrow \\

\backslash\text{leftarrow} & \leftarrow \end{array}\)\(\displaystyle \begin{array}{cc}

\backslash\text{s{q}rt\{3x\}} && \sqrt{3x} \\ \\

\backslash\text{frac\{2x\}\{3y\}} && \frac{2x}{3y} \\ \\ \\

\{\text{9 choose 3}\} && {9\choose3} \\ \\ \\

\backslash\text{overline\{AB\} } && \overline{AB} \\

\backslash\text{vec\{AB\}} && \vec{AB} \\

\backslash\text{hat\{AB\}} && \hat{AB} \\ \\

\backslash\text{cancel\{3ab\}} && \cancel{3ab} \end{array}\)