1. Khadgar's Pipe of Insight/Black King Bar: Protects you from spells, which help you survive alot better. Remember, Weaver's role is to survive!
2.Assault Cuirass: Give nice attack speed boost and armor boost, auras are nice too. However, it protects you from nothing but physical attacks, which, Weaver aren't afraid of. With the same gold, I'd rather get HoT.
3.Divine Rapier/Monkey King Bar/Buriza-do-Kyanon/Manta Style/Butterfly: Damage amplifier items, good on any carries.
4.Magical Bottle: Provides regeneration, taking advantage of Weaver's excellent Rune control ability. It is rather cheap. But it is just an optional (not extended) item nontheless.