NumberKey Free [Works with my Mac!]
If you use the Bluetooth wireless keyboard on the Mac, then you will be missing a number pad. You have a few options to get this – you can get a USB number pad, or look for a Bluetooth one… or use your iPhone / iPod Touch!
It requires installed software on your Mac, but I don’t find it too much of an overhead, and you can turn it on only when you need it.
At US$1.99, it’s far cheaper than going out and buying another piece of hardware.