Oh god, mental bondage! So hot.
And I have some fond feelings towards it, the first D/s thing I can remember doing during sex was mental bondage. The (then) boyfriend just pulled my arms up just past my head while I was lying down and ordered me not to move them. I can't even remember what he did after that, I just remember struggling not to move and being so incredibly turned on.

Definitely a favourite activity that doesn't get pulled out often enough for my liking. And I'm normally a squirmer!