A plot of the vector field F(x,y)=yx|Source=^−xy^{\displaystyle F(x,y)=y{\boldsymbol {\hat {x|Source=}}}-x{\boldsymbol {\hat {y}}}}. 

Self-made with Mathematica and MS Paint. Converted to SVG by 03:00, 21 July 2007 (UTC). Updated to reflect Mathematica 7.0 syntax and formatting Feb 17, 2011 (UTC).
Originally from en.wikipedia; description page is/was here.
Original uploader was Loodog at en.wikipedia