The X Window System (used on several modern unixes, including Linux) has something similar to the MS-Windows "Mousekeys" feature built in (part of something called AccessX). This lets you control the mouse cursor and generate clicks using the numeric keypad instead of the mouse.
To activate: at least on Redhat Fedora 9, shift-numlock. Your milage may vary, and there will be no notice, visual or otherwise, that the feature is activated. This is a toggle - doing it again will deactivate it. It'd be cool if this combo could be changed to a single key via xmodmap - something to look into.
- Keypad arrows move the mouse around
- slash, asterisk, and minus toggle whether button 1, 2, or 3 is selected
- the 5 key clicks with the selected button
- plus doubleclicks (not sure if it uses the selected button or always button 1)
- insert starts a prolonged click (if you want to drag-drop something)
- delete ends a prolonged click