As I'm such a kind and caring person, I recently uploaded two guides to the downloads section.
- A Game Design Document template. (Ideal for large mods/Indies)
- A Game Concept Document template. (Ideal for small m)
Both of these have been made by the guys at CONJURE, and they're probably the most complete documents that i've been able to find. They're really useful, and worth using as a developer.
You can find both of these downloads at the following links:
Note - I did not write either of these documents, they are provided as is, without any alterations on my part.