Is there a way to find out who I've dueled in the past or recently?

Diabolus1989

I've had some good duels but never remember who they were with.

GreyWolf_79

I hope not... I usually decline duels because I'm not into PvP, but I did accept one duel challenge from a particularly obnoxious low level because he was beginning to annoy me... I slaughtered the poor noob, but probably only because I had superior skills and gear. I'd hate to think that he's out there furiously grinding somewhere with some kind of obsessive vendetta against me, just waiting for the day that he can come back and kill me.

Tryxus

Only thing is a counter in your achievements. Don't think there is a way to see who you've dueled in the past...