Mike Love created an amazing visualization of philosophical influences using a program called Graphviz. The program gets its data from an open source tool called Freebase. Love started inputting information in Freebase in 2005. At the time of writing, it continues to be updated by other users. The visualization begins with Plato influencing Aristotle and explodes into an extensive mapping of influences. Here's a snapshot of the program:
The interactive visualization can be found here. Information on the project can be found here. A newer (though less dramatic) version of the visualization can be found here.