[Taqwus]

Some of the unholy sites let unholy priests enter to summon ghouls, mummies, possibly others (there are undead-summoning sites for shadows, CW undead, banes as well, but I think these might belong to death magic). The ghoul sites are of somewhat limited use to most nations as they're not likely to get any unholy priest other than a Mound Fiend, which can reanimate ghouls without a site at a similar rate IIRC.

I don't remember any holy site giving discounts or summons, just gems / unrest reduction / perhaps a local Purgatory (?), but I can't claim to have seen them all.