With all this talk of keyboard layouts...
...may I wave a flag for Microsoft Keyboard Layout Creator?
It's been around since the days of XP, but I've only just stumbled across it. Define your own keyboard layout on Windows - so I've now got lots of AltGr-combinations for things like ° µ Ω ✓ ⌘ ½ → and dead-key combinations for óôòöõ.
Wonderfully geeky fun.