I have to agree with the posters above; utilizing existing hardware is defiantly the way to go.
If you want to do something "creative", you can buy a relatively cheap miniature laptop wireless mouse.
These mice are usually smaller then game controllers, and their contents tend to be project-box friendly.
Such devices work on batteries, and replacing them once in a few months can get tedious.
Keep in mind that some mice support rechargeable batteries. This feature will allow you to recharge your "foot-pedal"-like device when it's not used, thus eliminating the "problem" described above.
As far as the software part's concerned, if you're going to be using this little gadget on anything that's [>= WinXP], you're in luck – it's actually very easy to read raw input from HIDs.This is rather convenient because you will not have to bother with writing a device driver - a relatively simple Win32 application is all that's required to get this to work.
In case you're wondering how your application can distinguish between device-events: Windows allows you to enumerate such devices. This means that each recognizable HID has a unique handle which can be used as a filter when you handle the WM_INPUT notification in your message handler.
I hope that this was helpful. =)
P.S.
Please excuse any grammatical errors,
English isn't my first language.
