USB Keypad Hackery
I made this a few weeks ago. Coding on my laptop is a real PITA without a full keypad (not for the numbers but for the cursor and page movement), so I hacked a couple keypads to make one. Every separate keypad you can buy is a full-size keypad and I wanted something smaller that I could place over the laptop's existing cursor keys. There's a mouse/keypad combo available on ebay that had what I needed, but I needed to ditch the mouse part. I took apart a separate IBM full-size numeric keypad and wired the one from the mouse to it. The circuit layouts aren't the same so not all of the keys work, but all of the important ones do with the exception of the Ins key (it works, but it gives me two keypresses every time I press the key).
The little box has the circuit from the IBM keypad. The heavy cable is from an old ThrustMaster joystick I had that I used because it had ten wires going through it. I have a small circuit in the box also that is supposed to fix the Ins key, but it isn't working right yet. Otherwise, the pad works very well.
It's a real shame that no one makes a separate small keypad instead of just the full-size ones that you can clip to your laptop like this. I'd think that a lot of people would be interested in one.