To the OP: the bottom line is that no, there is as yet no single device that does all of the things you ask. If you really want do all three functions (external display, external keybaord/mouse, external HD), then you need to buy all three discrete components separately.
FWIW, I have a similar setup. When I'm at my desk, I have an Apple Keyboard and Mighty mouse, that I plug into one USB port on my MBP. I did this primarily because, to be honest, I don't trust the on-board keyboard to last very long. It feels incredibly flimsy and I just get the impression I have to baby it and use it as little as possible (though when I'm out and about, I of course have no choice but the use it).
On the FireWire 800 port, I have
one of these bad boys hooked up, so that when I'm at my desk, I can do some heavy lifting in terms of video editing and work with high res images and other large files. Though usually when i'm on the road, the 200GB internal drive is plenty good.
I do, however, use the built-in display regardless of where I am. It's a good enough display, no need to duplicate its functions.