BMP World Gen
This plugin requires WorldGeneratorApi to function.

Bukkit plugin to set biomes in your world while maintaining the natural generation! When freshly generating a new world this plugin allows you to draw a BMP image with certain color codes in order to control biome placement. Every 4x4 block section outside the image will either be set to a default biome or you can set the image to be tiled.

NOTICE: If you remove the plugin from the server the world generation will return to normal outside the image area, but there will be obvious chunk walls. A mountain biome might make it look nicer, but there appears to be no way to get the original biome that should be placed there.

Configuration details, examples, and how to make the BMP images available at the github page.

Example
There are more images on the github page, but here is one of the examples: