NodeXL offers a range of shapes to represent vertices, including: circle, square, triangle, and diamond in filled and unfilled forms.
Vertices can also be represented as images.
Edges can also have styles:
More networks from Slate: Interesting use of network diagram for data display
Here is an interesting use of a network diagram for data display:
Readers Who Like This Apocalypse Also Preferred …
The end-of-America social network.
Slate’s “Choose Your Own Apocalypse” game asked readers to browse
through a list of 144 end-of-America scenarios and choose up to five
that seem most likely to wipe the United States off the map. The
scenarios our readers chose fell into patterns. Those who chose
“Laziness,” for example, were also likely to choose “Decadence” and
“Overpopulation.” Those who selected “Theocracy,” meanwhile, were also
likely to choose “Intelligent Design.”
To help visualize those correlations, we’ve arranged the scenarios
into a social network. Two scenarios are connected if at least 5
percent of users voted for the pair as part of their end-of-America
menus. The less-popular scenarios on our list of 144 tended not to be
associated with any others. What you see here, then, are the 82 that
have at least one connection to another potential America-ending
scenario. Mouse over any icon to see its title and connections.