VisualisingData has a great list of visualization tools, ranging from the big dogs (R, Processing) down to the lesser-known guys (Mondrian, D3) that winds up being a great starting list for anyone looking to get into the data visualization space.

This second part presents the prominent and powerful data visualisation programming languages and environments that dominate the creative engineering that sits behind today’s design output

via Visualising Data » Blog Archive » Part 2: The essential collection of visualisation resources.