Got this out of the necro forum on stratics:
Horde Minion requires 30 Necromancy and 30 Spirit Speak. Abilities: Pack animal, picks up stuff, decent combat assistant.
Shadow Wisp requires 50 Necromancy and 50 Spirit Speak. Abilities: negative energy flare; periodically heals the mana of those friendly to the caster (and the caster) IF they have negative karma. the more negative the karma, the more mana you get back.
Dark Wolf requires 60 Necro and 60 Spirit Speak. Abilities: +1 stamina every 2 seconds. Wolf mastery; allows you to tame any wolf as if it were a 0 difficulty tameable.
Death Adder requires 80 Necro and 80 Spirit Speak. Abilities: Snake charming; you can command any snake to attack a target to which you can do negative acts. You don't get credit for the kill, however.
Vampire Bat requires 100 Necro and 100 Sprit Speak. Abilities: all melee damage it does will heal it's master (You!) for an equal amount.
Familiars can't be commanded like pets. They do join in the fight automatically when you're attacked by something agressive... most of the time? All of the Familiars will invis with you.
Information Provided by evilmoocowgod