I see a lot of people praising tenkeyless but I use the numeric keypad so often I can't bring myself to buy one, even if my current keyboard uses more space.
My keyboard and mouse are actually pretty far apart from each other so for me a dedicated keypad on the left wouldn't really work, especially since when i use it i do so mostly with my right hand.
Interesting suggestion though, it hadn't crossed my mind yet to try that.
In the past I've often worked with my mouse to the left. But when I do that I like to switch the mouse buttons as well, and then it's a hassle when someone else uses the mouse. Nevertheless, it's an option.