\documentclass[a4paper]{article}

\usepackage{pgfplots}

\begin{document}

\begin{tikzpicture}
\begin{axis}
\addplot3[contour gnuplot,domain=0:1] {x*y}
	[pos segment=0] node[pos=0] {0: 0} node[pos=0.5] {0: 0.5} node[pos=1] {0: 1}
	[pos segment=1] node[pos=0] {1: 0} node[pos=0.5] {1: 0.5} node[pos=1] {1: 1}
	[pos segment=2] node[pos=0] {2: 0} node[pos=0.5] {2: 0.5} node[pos=1] {2: 1}
	[pos segment=] node[pos=0,fill=red] {*: 0} node[pos=0.5,fill=red] {*: 0.5} node[pos=1,fill=red] {*: 1}
	;

\end{axis}
\end{tikzpicture}

\end{document}

