The dependency:tree goal of the Maven plugin dependency
supports various graphical outputs from the version 2.4 up. This is how
you would create a diagram showing all dependencies in the com.example
group in the dot format:
mvn dependency:tree -Dincludes=com.example-DappendOutput=true -DoutputType=dot -DappendOutput=true -DoutputFile=/path/to/output.dot
To actually produce an image from .dot you can use one of .dot renderers, f.ex. this online dot renderer (paste into the right text box, press enter).
You could also generate the output f.ex. in the graphml format & visualize it in Eclipse.