Bukkit

8/5/12: Initial upload
8/20/12: Added many new configuration options, including full config of offers which villagers generate, and compatibility with Shopkeepers.

If you have this plugin, Shopkeepers, and a third plugin which can create villagers (VoxelSniper is an example), consider looking into the config.yml's section on Shopkeepers. If you configure these numbers to be too low, and use the third plugin to spawn a villager while your server is badly lagging, a crash may occur. I am going to discuss this with the creator of Shopkeepers; hopefully it can be corrected.