Arrow symbols. 

\leftarrow              \rightarrow
\longleftarrow          \longrightarrow
\Leftarrow              \Rightarrow
\Longleftarrow          \Longrightarrow
\hookleftarrow          \hookrightarrow
\leftharpoonup          \rightharpoonup
\leftharpoondown        \rightharpoondown
\rightleftharpoons      \leadsto
\leftrightarrow         \longleftrightarrow
\Leftrightarrow         \Longleftrightarrow
\mapsto                 \longmapsto
                \uparrow
                \downarrow
                \Uparrow
                \Downarrow
                \updownarrow
                \Updownarrow
                \nearrow
                \searrow
                \swarrow
                \nwarrow