I used to have Keyclone a long time ago, couldn't help you setting it up. I'm sure things have changed.

But I did try a warlock/priest combo. It worked very nicely, and probably still is one of the best 2 class combos. I used an affliction lock as the lead toon. Dot everything that moved, and the priest followed around with bubbles, renew, shadow pain if needed, etc. I could see a druid/lock combo working well too.

A paladin/warlock combo used to be nice. Paladin gathers mobs while mounted, then tanks while the lock spams seed of corruption, etc. This was back in the Burning Crusade era.