Minecraft wiki entry for Biome, associated text: A very old image of biomes work-in-progress, you can clearly see that biome grass colors have not been implemented at this point.
The biomes graph prior to Java Edition Beta 1.8, drawn by Markus Persson. Notice the chicken scratch handwriting, as Notch was working quick to try to get the biomes added by the Halloween Update (Beta 1.2).
The old biomes graph with linear axes that was applied before Java Edition Beta 1.8.
A biome map tweeted by Notch.
Notch took this screenshot while testing a revamped river biome.
The first image of a giant tree taiga, as tweeted by Jeb.
This is the first picture provided of the badlands biome (then called mesa).
The first image of a stony shore (then called cliff) biome, provided by Jeb.
Jeb's first image of the jungle biome.
Jeb's second jungle teaser screenshot.
Biome colors template for Java Edition 1.7 and 1.8.