Resident Nodes
Usually represented as Ovals, but circles or rounded rectangles are fine.
Input Nodes
Any shape that has a flat top side linked to a smaller flat lower side by equal, balanced, continuous (i.e. no breaks) sides will suffice. The prefferable shape is on the right side below.
Context Nodes
Use a flat-based pentagon such as the one on the right below. A rounded top is also acceptable.
Decision Nodes
Virtually all literature available on decision theory depicts decision nodes as rectangles.
Utility Nodes
Hexagons are the preferred implementation, but parallelograms such as the one depicted below can be accepted
MTheories 
