This came up during a combat last week. The party had barricaded themselves behind double doors and the wizard was peering through the keyholes, dropping Scorching Bursts on anything foolish enough to enter his vision. While I readily admit that the "Sorcerer Tim" aspect of this scenario is entertaining and did make for a good encounter, I wonder what the rules are for ranged magic and its necessity for line-of-effect.
Is there a hard and fast rule on how to determine whether a spell requires line-of-effect or not? For instance, I wouldn't have allowed a Fireball or an Acid Arrow to have been cast that scenario simply because my understanding of how the spell manifests would not allow it to function in that fashion. Some of this is vaguely addressed in the PHB section on combat regarding cover and concealment, but none of it is explicitly laid out.