Here's one way to create a fogless version of a shader.

1. Download the source code for the built-in Unity shaders.

2. Open the .shader file for the shader you want to modify. Copy the contents.

3. Create a new shader in your project (Assets->Create->Shader). Open it for editing.

4. Copy the contents of the built-in shader into your new shader file, overwriting the default contents.

5. Rename the shader. For example, if you are de-fogging the diffuse shader, change the first line from Shader "Diffuse" to something like Shader "Diffuse Fogless".

6. Find the line which controls the fog. Most likely it will say Fog { Color [_AddFog] }. Change it to Fog { Mode Off }.

7. Save your custom .shader file. Now you should be able to select your shader from the drop-down attached to any Material.