ZGRViewer is a 2.5D graph visualizer implemented in Java and based upon the Zoomable Visual Transformation Machine. It is specifically aimed at displaying graphs expressed using the DOT language from AT&T GraphViz and processed by programs dot, neato or others such as twopi.
QuickGraph 2.0 provides generic directed graph datastructures and algorithms for .Net 2.0. QuickGraph comes with algorithms such as depth first seach, breath first search, shortest path, network flow etc... QuickGraph supports GLEE and Graphviz to render the graphs.