Either with complex event systems or on the technical side of things, who has shown a knack for pushing the engine? Note that this is not for scripting!
Providing screenshots / links or other examples may help your nominee's chances!
Exhydra
Most people who show great mechanics have been using scripts these days, so it's hard to think of many people for this. I know Exhydra already has my vote.
Yeah, I third the Exhydra nomination. I know a few other people tat do a lot of eventing, but they're either on another forum (chaos project has some decent eventers), or it would be a self nomination for my cheat code system, which none of those are valid. My only regret is that without being here as much as I should be, I haven't been able to test out everyone's demo, so I don't know just how everyone did =p