tkz-euclide arrives on the ctan servers. You can get it with ftp from dante.de
ftp://ftp.dante.de:21//pub/tex/macros/latex/contrib/tkz you need to install tkz-base and tkz-euclide. These packages work only with pgf 2.1
\documentclass{article}
\usepackage[upright]{fourier}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{tkz-euclide}
\usetkzobj{all}
\definecolor{fondpaille}{cmyk}{0,0,0.1,0}
\pagecolor{fondpaille}
\color{Maroon}
\tkzSetUpColors[background=fondpaille,text=Maroon]
\thispagestyle{empty}
\begin{document}
\begin{tikzpicture}
\tkzDefPoint(0,0){A}\tkzDefPoint(6,0){B}
\tkzDefPoint(6,4){C}\tkzDefPoint(0,4){D}
\tkzInterLL(A,C)(B,D) \tkzGetPoint{I}
\tkzDrawPolygon (A,B,C,D)
\tkzDrawSegments(A,C B,D)
\tkzMarkRightAngles[fill=Maroon!20,size=.3,opacity=.5](D,A,B A,B,C B,C,D C,D,A)
\tkzDrawPoints(A,B,C,D,I)
\tkzMarkSegments[mark=s||](I,A I,B I,C I,D)
\tkzLabelPoints(A,B) \tkzLabelPoints[above=6pt](I)
\tkzLabelPoints[above right](C,D)
\end{tikzpicture}
\end{document}

Best regards
Alain Matthes (author of tkz-euclide)
There are a lot of examples on my site altermundus.fr