• box
• polygon
• ellipse
• oval
• circle
• point
• egg
• triangle
• plaintext
• diamond
• trapezium
• parallelogram
• house
• pentagon
• hexagon
• septagon
• octagon
• doublecircle
• doubleoctagon
• tripleoctagon
• invtriangle
• invtrapezium
• invhouse
• Mdiamond
• Msquare
• Mcircle
• rect
• rectangle
• square
• none
• note
• tab
• folder
• box3d
• component

Aquí unos Samples.

http://graphviz.org/doc/info/colors.html

<graphviz>
digraph test {
this [shape=doublecircle];
is [shape=box];
a [shape=invtriangle];
test [shape=polygon,sides=6,color=red,style=filled];
{ rank = same;
this; what;
}
this->is;
is->a;
a->test;
test->what;
what->do;
do->you;
you->"think?";
}
</graphviz>