Following your suggestion, the MEs I would particularly like to see would be replacements for the SEs normally used with the balloon icons. (Hmm, maybe this means that technically I'm asking for SEs, but read on!) I think if I have to hear another game with that same one used for the exclamation mark I shall do something drastic.
So the 3 most used would be:
Exclamation mark
Question mark
Lightbulb/idea dawns.
I accept, though, that doing something actually musical for such short sounds may not be practicable. But in my mind I was thinking that a gong could be the basis of one of them, a trumpet chord might be another. Dunno. But as you seem to relish odd requests, I thought it worth a try.
Also a new Inn/sleep ME, maybe even a couple, would be nice.