So, a few times now I've had that moment where, after building my base up, I was unable to see where I'd put my commander. Given that it's the most powerful builder unit I have, this was a bit of a problem. A simple button that instantly selects your commander, wherever they might be, would be a REALLY good idea, I think. Additionally, something to let you select idle engineers would also be nice, as you could then assign them to whatever needs doing at that particular moment. Another suggestion I have is to allow you to set factory waypoints through teleporters. It's not quite as vitally needed as the suggestion above, but it's something that I've more than once felt would help to tidy up my base.
Until they put something proper in the GUI the default hotkey is C, double tap to go straight to him.