Minecraft wiki entry for Eye_of_Ender, associated text: A super-easy stronghold triangulation tool
JSFiddle Eye of Ender triangulator - can guess the location of other 2 strongholds in the first ring
Minecraft Stronghold Locator Eye of Ender throw plotting visualizer - zoomable to show all possible stronghold rings
Python Eye of Ender throw plotting tool
HTML Eye of Ender throw plotting visualizer (not updated after 1.9 stronghold placement changes)
Chunk Base Stronghold Finder (seed-based)
Amidst - File-based world visualizer
Find strongholds by analyzing stronghold.dat file