Draw an angle on tikz plots (LaTeX)

tikz-anglearc.tex

% draw an angle arc on tikz plots
%
% #1: A point of ∠ABC
% #2: B point of ∠ABC
% #3: C point of ∠ABC
% #4: arc radius (length units)
% #5: arc style (e.g. fill=red!50!white or draw)
% #6: label
%
% Issues:
%   * avoid polluting coordinates' namespace (name clashes)
%   * make it more tikz-ish
\newcommand{\anglearc}[6]{%
%
    \begin{scope}
      \coordinate (AngleArcA) at (#1);
      \coordinate (AngleArcB) at (#2);
      \coordinate (AngleArcC) at (#3);
      \path [clip] (AngleArcA) -- (AngleArcB) -- (AngleArcC) -- cycle;
      \node (AngleArcCircle) [#5,circle,minimum size=#4] at (#2) {};
    \end{scope}
    \coordinate (AngleArcA1) at (intersection of AngleArcB--AngleArcA and AngleArcCircle);
    \coordinate (AngleArcC1) at (intersection of AngleArcB--AngleArcC and AngleArcCircle);
    \draw ($ (AngleArcA1)!0.5!(AngleArcC1) !-1.1! (AngleArcB) $) node {#6};
%
}

I wrote this macro before I discovered tkz-2d (http://www.texample.net/tikz/examples/tkz-2d/) which seems to be more versatile. See also: http://old.nabble.com/tkz-2d-td12645741.html