Here are several plots of surfaces - the lines in the plane below represent the contour plot for the surface!  This is a nice feature of MATLAB's mesh plotting routine - it automatically plots the contour along with the surface (notice that the heights corresponding to contours are color coded rather than labeled with numbers)

z = x^2 + y^2	z = xy
z = cosx*cosy	z = e^x siny
z = xycosxsiny	4z = 3x + 5y
z = sin(xy)	z = e^x sinx
z = sqrt(x^2 + y^2)*cos(x^2 + y^2)	z = cos(x^2 + y^2)sin(x^2+y^2)