Just finished building this Lego siege tank. It's fully remote controlled (driving and siege/un-siege). I added a bit of audio from the game to make is sound a bit more authentic.
Edit: I've started a parts list. Only the power functions parts are on there so far. I'll add more as I have time. It'll be a looooong list.
Here's a short video of the tank's guts. It shows the two drive motors and the mechanism for moving the tracks out for siege mode.
I've been wanting to make a remote controlled Colossus but I don't know how, so I'll just have to wait until some fan with engineering skills makes one and stare in awe.