vsfplot is a 2D vector and scalar field plotter. It features Line Integral Convolution (LIC) on data, curvilinear scaled arrows following the flow lines, a mixed mode (scalar field map with overlaid vector field), handling of missing data to not interfere with the flow lines, generation of Scalable Vector Graphics (SVG) files (which are easily editable and convertible while preserving the best quality for inclusion in a PDF scientific article), and a color palette designed so the flows are uniformly readable when printed as greyscale.
GTKMathplot is an interactive plotting program based on GTK+ and the Cairo graphics library. It can display bidimensional curves, tridimensional curves, and surfaces from Cartesian or parametric equations describing the mathematical objects you would like to visualize. It is designed to be intuitive for high school students with good mathematical knowledge. University students of engineering, physics, mathematics, or natural sciences should need no explanation at all to start using it proficiently.