Cenarion Expedition: This is the first neutral reputation. You will encounter them in the form of a small camp of Tibia Gold quest-givers near the entrance to Zangarmarsh in western Hellfire Peninsula.
The bulk of them are in the town Cenarion Refuge in the east of Zangarmarsh. You can increase your reputation by questing, doing repeatable quests and killing Naga in Zangarmarsh or in one of the Coilfang Reservoir instances.
Sporeggar: The Sporeggar have a little town in eastern Zangarmarsh. They are mushroom-like creatures. Increasing your reputation with them is possible through several different quests per reputation level.
Up to a certain point you receive 15 reputation points for killing mobs in and near the dead mire as well as at the spawning glen.
The Consortium: A relatively big reputation in Outland, comprised of the Ethereal race (Energetic Mummies).
The Consortium is interested primarily in trade. Increasing your reputation with them can be done through repeatable quests, taking place in Nagrand and Netherstorm.
Killing mobs in the Mana Tombs (an Auchindoun instance) will also up your rep.
Scale of the Sands: Little is known about this one. It is believed to be related to Mount Hyjal, the toughest and hardest to reach raid zone in Outland.