This one is for Finale users, and possibly Sibelius users.
In Finale, you can enter musical notation into a score using only the computer keyboard in a mode called "Speedy Entry" which relies on the numeric keypad to input the duration of each note.
I'm learning Finale on my desktop Macintosh, which has a full keyboard. But I had to go out of town for a week.
To take on the road, I installed my second license for Finale on my wife's Dell laptop running Windows XP. However, the Dell, like almost all laptops, does not have a separate numeric keypad next to the QWERTY keys.
So how to do Speedy Entry on a laptop?
I went to a local computer store and found an Inland USB full-sized external numeric keypad for only $10. You just plug it in and it works--no drivers, no external power supply, no fuss.
The Inland design has full-sized keys on a base that is rather thick, which means it lines up very well next to the regular keyboard built into your laptop. There are other models that are smaller, thinner, and more expensive, but the Inland was a perfect fit for me.
This is the best $10 I ever spent on a computer gadget.