Definately take lightning tree, the passive is very good. I don't know what is the best combination, but try to mix and match and you'll find one you like. All the trees have their plusses. I respecced my sorc from light/poison to light/cold recently, that seems to work out really well for me. The passive gives +%life and a huge flat boost to my defence, which then gets multiplied by the lightning passive. Right now I have nearly 700k with the ice elemental aura.
Edit: Oh and Archone, sacreds are indeed the last tier as said. There are loads more than 1-6 uniques, more than one per base item. And sacreds can't be made with the cube recipe