some of build-in shapes for node

shapes.gv

digraph G  {
label="some built-in shapes";
box [shape=box] ;
polygon8 [shape=polygon,sides=8];
point[shape=point];
egg [shape=egg];
triangle[shape=triangle];
diamond[shape=diamond];
circle[shape=circle];
square[shape=square];
box3d[shape=box3d];
note[shape=note];
tab[shape=tab];
folder[shape=folder];
component[shape=component];
triangle->box->square->diamond->polygon8;
point->egg->circle;
note->tab->folder->component->box3d;
}