I posted a very similar post in my other blog Find Aeonaxx devoted to finding the rare spawn Aeonaxx in Deepholm. I cannot stress enough that NPC scan is an absolute necessity if you plan on hunting rare spawns. I have tried other addons with the same purpose, but I always come back to NPCScan. You can download it from Curse.com. I also highly recommend downloading NPCScan.Overlay as well. (NPCScan.Overlay adds an overlay to your map which displays where rare mobs patrol.) In the screenshot below you can see an example of this. The colorful areas are where different rares can be found, and in the bottom left hand of your screen it will tell you the name of the rare spawn using a nice color code to tell you which mob patrols in each area. When a rare is found you will be able tell the approximate location that it has been found right on your map because a small, almost transparent circle will appear in the color associated with the particular npc. As you can see below I found Shok'sharak in the western spawn location in Promontory Point.
What NPCScan does is track rarely seen mobs in the game by proximity. When a rare npc is found npcscan checks your creature cache and the mob becomes "cached". It is extremely important that you clear your cache often. Npcscan will NOT be able to find a cached npc again until your cache has been cleared. Although kind of annoying, clearing your cache is relatively simple.
