$\begin{pmatrix} 0 & 1 \\ -1 & 0 \end{pmatrix}$ (rotation by $-90^\circ$)

$\begin{pmatrix} 0 & -1 \\ 1 & 0 \end{pmatrix}$ (rotation by $90^\circ$)

$\begin{pmatrix} 1 & 0 \\ 0 & -1 \end{pmatrix}$ (reflection across $x$-axis)

$\begin{pmatrix} 0 & -2 \\ 1 & 0 \end{pmatrix}$ (scaling and rotation)