A couple of ideas.
* Warlock: as mentioned above, this takes little work.
** Dragonfire Adept: as warlock
* Spirit Shaman (OA or Complete Divine): a priest who deals with spirits
* Incarnate or Totemist: soulmelds representing the various Loa?
* Binder: I don't know this class very well, I've only dabbled with it. But seems almost perfect.
* Wilder: see below...
Many years ago I joined a campaign that had some focus on the local druids and issues with the Fey. I don't remember the full party comp when I joined, but there was already a druid and a warlock (two of my favorites) and the DM didn't want just more of the same.
I talked him into letting me play a Wilder (he had distrust of Psi due to it's wackiness in 2e and never embraced it for 3e) with the notion that all of my psi powers are entirely reflavored into "spirit magic".
The PCs were already searching for a mad hermit who was in exile from the druidic grove for weird taboo practices and the DM tossed his NPC notes to let me fill that role. For reference I used the FRCS picture of Halaster Blackcloak.
Examples
* Psi-Crystal: a bird-skull, usually worn as an amulet. At higher levels it could float around on its own or manifest "legs" like some sort of creepy birbskull-spider.
* Wild Surge: voodoo is chaotic?
* Mind Thrust: "Evil Eye" sort of a Power Word Kill style effect. Sometimes just an intense glare, other times actually telling them to "Die!".
** So mind-thrust is all or nothing. Fat dmg or 0. One of my shining achievements in the game was landing a maximized mind-thrust ("No, seriously, F'n DIE!!!") on a Green Dragon that was a little above our pay-grade. IIRC, 110dmg (level 7, Wildsurge +4? for 11d10, max).
* Vigor / Share-Pain (w/psi-crystal): Invoking the spirits to protect me. Ablative shielding is good.
* Astral Construct: conjuring spirits of the slain to fight for me. I always shaped the construct into the form of something I'd killed with my "evil eye".
As its been nearly 20yrs, I can't remember all of the details, but hopefully the above made some sense. I was the only one at the table with any experience with 3e Psionics and the rest of the players had no idea wtf I was doing or how. The DM loved it.