I'd like to remap Caps Lock to right click - for the cases where I can focus on objects with cursor keys, or tab.
For instance after selecting files in Finder I'd like to hit Caps Lock and get the contextual menu you'd get on right click.
You can use BetterTouchTool for this. Just create a keyboard shortcut which is bound to right-click.
There are to caveats, though:
I'm not sure if there is any way to invoke the context menu on the focused element rather than wherever the mouse is. However, if you do find such a way to do this, you can use a combination of KeyRemap4MacBook and PCKeyboardHack to rebind it to CapsLock.
The 3rd party tool http://pqrs.org/macosx/keyremap4macbook/ seems to be able to do what you need to remap your keys.
One possibility is to remap Caps Lock to Control and thus pressing Caps Lock + left-click would open the context menu.
Sure, this doesn't remove the need for a mouse click, so the right-click might be a better solution :)