Speak With Animals
Since my PC is a Ranger, I prefer the
Speak With Animals spell, if the GM doesn't hate it (Piratecat does). It allows me to interrogate, and ask for aid from, creatures that would not otherwise be of any use to the party, better communicate with my Animal Companion, and gather information that might otherwise be inaccessible to the Druidless party... I can ask a bird to carry a message for me (even without the higher-level
Animal Messenger spell, although I risk getting a "No"), I can ask the local birds and squirrels if they saw the (X) pass by here, I can ask the gutter-rats if they know who killed this person lying in their gutter, I can ask the local Bear if there are any Fey nearby, ask the shivering rabbit why it's scared, etc.
This is further helped by Wild Empathy, as the +Level bonus to Diplomacy attempts, to befriend or convince an Animal or Magical Beast (at a -4 penalty), can greatly aid such attempts.
Speak With Animals, used in conjunction with Wild Empathy, should probably grant AT LEAST a +2 Circumstance Bonus, and that's in addition to the +4 when dealing with the Animal Companion.
Another use is in teaching an Animal Companion something complicated, which would ordinarily be beyond their intellectual capabilities. By carefully explaining it to them, you can enable them to perform complex tasks, such as going over to the hook on the wall, and bringing you that ring of metal keys, while being as quiet as possible, so as not to awaken the sleeping Ogre guarding the cell your party is stuck in, for example!