[hnbad]

I use WinCompose, which is a Windows implementation of an XCompose style compose key. It comes with a number of composition sequences but you can also add your own. I have mapped it to the "menu" key which I never use so "ñ" is <Menu>,<~>,<n> or <Menu>,<n>,<~> (both work by default).

For acute/grave accents I have a dead acute/grave key on my keyboard and because it's a German layout I already have the umlauts as separate keys. For "ë" and such I can compose the letter with <"> to get the diacritic version.