Something that's missing in 3rd Edition 40k is the selection of "wild animals" from the Rogue Trader book. These beasties could be amusing, annoying or just damn crazy, always getting involved at the wrong moment.
Incase you've never read Rogue Trader I'll explain a bit. RT had a lot more of a role-playing aspect to the game, it was still a wargame but it had a lot more options and was very open ended. One of the things it took into account was that planets have indigenous life forms, not of all these creatures would be from the main races, some would be wild... There was everything from telepathic cats to dinosaurs, aswell as some creatures you'd recognise today. Infact the original Genestealers were just a monster used to stir things up in games or perhaps for special scenarios.
So how can we bring some of these beasties into 3rd edition? Well first off we don't want these creatures to have such an influence on the game that they decide who wins, rather they should be a hinderance or perhaps a little bonus. Also they should be random, players should not control them or if they do not for long.
Since moving house, I've not been able to find my copy of Rogue Trader, so unfortunately I've not been able to convert the creatures from it into 40k. But soon as I track it down I'll get that sorted and uploaded. For now I'll write up what we use instead, what models we use and how it works.