I would like to bake just the texture colors while using cycles. In blender internal I would pick "Textures" as bake type to accomplish this, but no such option is available in cycles. According to the documentation it seems the 'UV' bake type should do this but instead it seem to bake the uv coordinates or something like that.
Edit: I would like to clarify the use case. I have a game level that we normally bake with lots of lights using cycles which takes the order of 10 hours with lots of complex materials. We can also lower the samples / bounces settings to get a quicker, noisier result. But, we would also like to render just the the unlit texture colors to get a super fast, noiseless, flat version to see what textures will look like in the level. This is useful when we iterate the source textures frequently and the designers prefer this over the noisy version.
So ideally I would like to modify the materials as little as possible (not at all). It is certainly an option to have a script in our plugin modify them automatically, making the materials shadeless as suggested below, but that would turn the whole thing very complex which I would like to avoid.