I'll start us out. I have a black mage in a heavily houseruled game. My lineup looks like this:

Fire spirits - Demonic footsoldiers, tall and imposing with leathery bat wings, skin the color of recently dried blood (very dark red). Girded in armor of black leather and blackened steel, wielding whips of flame. Their energy aura takes the form of a heat shimmer around them, so hot that it causes flammible objects to spontaneously burst into flame when in close proximity. Their elemental attack could be staring at something until it spontaneously bursts into flame, pointing at something and having a fireball streak towards the target, or striking something with their whips. Their engulf would be represented by wrapping their whip around a target, the whip's coils visibly constricting over time. Fear would be the full weight of demonic gaze; noxious breath would be a massive belch of brimstone-infused halitosis. Prolonged exposure to water burns like acid.

Guidance spirits (Detection) - Demonic scholars, secretive and terrifying. They speak in insidious whispers, and know your darkest desires. Very jealous of their knowledge, it must be forced out of them or purchased with knowledge of equal value. They can be bribed to turn on their summoner with an offer of knowledge they do not possess.

Sewer spirits (Health) - Based on Sludge spirits (Street Magic 146). Remove anaphylaxis and corrosive spit from list of powers. They appear as a creeping pool of sewage, similar to the pokémon Muk, but with hollows instead of eyes. Their Engulf power does Stun damage, except for great form sewer spirits using their LoS (A) Engulf, in which case their victims sink into the ground or floor (or suffer the floor creeping over them, or a hill or tree swallowing them up, or the like) and take Physical damage, buried alive. Their Movement power only applies to movement on the ground or on/in the water (it can't be used to aid flying). Elemental Attack is essentially throwing poo. They retain a sludge spirit's severe allergy to clean water, but not to clean earth. While based on sludge spirits, sewer spirits are twisted, not toxic - their signatures are darker than the norm, but not toxic enough to bring down a bounty on my head.

Smog (Illusion) - As Smog spirits (Air spirits with Concealment and Confusion replaced with Noxious Breath and Weather Control [Acid Rain, Pall of Smog]), and with Severe Allergy (Fire) (It burns up all their oxygen). As their name suggests, they appear as hazy clouds of polluted air. Their Elemental Attack power uses the Smoke elemental effect (Street Magic 165) instead of Electric. Their signatures are darker than the norm, but not toxic enough to bring down a bounty on my head.

Tricksters (Manipulation) - As Harrows (Street Magic 145). They appear as whatever they feel like: a bum clothed in rags, a mangy coyote, a businessman with an air of menace. Anyone who sees through a trickster's trick (resists its Accident, Confusion, Desire Reflection, Fear, or Influence powers, or any illusion or mental manipulation gained through Innate Spell) is immune to all of those powers for (60 - Spirit's Force x 5) minutes. Otherwise as Harrows, but twisted, not toxic - their signatures are darker than the norm, but not toxic enough to bring down a bounty on my head.

I haven't fleshed them all out yet--but I've defined several of my voodoo priestess's favored spirits in terms of particular Loa.

Guardian--The Iron Warriors of Ogoun, patron of smiths, a being associated with fire, iron, and war (among other things). Astrally, they appear as powerful, musclebound men, usually wielding a hammer. Binding rituals involve offer and acceptance of rum or whiskey and tobacco to vessels ridden by the spirit for the purpose.

Guidance--The Old Men, spirits in service to Legba, the Opener of the Way. Very much the Old Man at the Crossroads, in several senses. Astral appearance is about what you'd expect, an old man in a colorful robe, though individual features vary with the spirit. Binding rituals involve the ceremonial sharing of a pipe.

Man--The Ladies, who serve Erzulie, spirit of love and beauty (and again, other things). Their astral appearance is quite human, and very beautiful. Binding rituals involve sacrifice of perfumes, sweets, and liqueurs...and occasionally other bargains. The Ladies can get one spell from among those the priestess knows, and having grown up in a bordello, she's quite well-versed in the Orgy spell.

Water--I haven't settled on details, but probably associated with Agwe. If so, the customary offering in rituals would be champagne.

Task--I haven't decided on an appropriate form for task spirits. Children of Zaka, perhaps, though for all his hard-working nature, that spirit is associated principally with agricultural tasks, and does not like cities or city-dwellers. I may decide that task spirits are associated with different Loa, depending on the nature of their tasks; many of the tasks my character would call upon them are probably more suited to spirits related to Ogoun.

Watchers--I haven't connected watchers with any particular patron. I visualize them as a pack of street urchins on the astral.

Mona Lisa Overdrive by William Gibson has some great possession-based voodoo spirit descriptions, if you need any inspiration.