A couple of notes included on why these spells are considered rare. Probably missing a lot. Most of these combines need a piece of parchment and a quill. Priest spells can be combined by any int caster; int caster spells only by members of the same class as can use the spell.
Levitation: dew clover, Yaeth’s 70 left (enchanter only: Yaeth 65 left and right)
Everlasting Breath: sliver of moonstone, Yaeth’s 50 left (enchanter only: Yaeth’s 63 left and right)
Lots of classes, each drop only from one rare mob (in the Deep, I think).
Remove Greater Curse: Yaeth’s 73 right, words of apparition
Arch Lich and one of the Rhags in Ssra. Can also be bought in N Ro LDoN, 800 points.
Several general enchanter spells drop, but are uncommon – Forlorn Deeds, Augment. Go to Skyfire, or the kobolds in Velks (depending on which expansion the spells were released in).
Illusion Vah Shir: Keris 7 left and right
Drops only from the Shissar Assassin in Ssra, needs a rogue to access the room.
Dead Men Floating: words of agony and asylum
No, not Dead Man Floating, the group version.
Augmentation of Death: words of anguish and expedition
Demi Lich: words of awareness, revenant, tenancy
Despite being a level 56 spell, this used to be level 60, and still only drops from level 60 mobs in Kunark.
Gangrenous Touch of Zum’uul: words of abrogation, constancy, distress
Drops from 2 mobs in Chardok; only marginal use.
Word of Redemption: Yaeth’s 114 right, Yaeth’s 108, rune of conglomeration
Divine Intervention: Toharon 21 left, Toharon 22, words of recourse
Both level 60 Kunark drop spells.