Okay - I've been digging deep, and this is what I've dredged up:

Crission's Pixie Strike:
A lot of you have noticed that you get resist after resist with Pixie
Strike, until it "takes" - then it suddenly works over and over (ditto with
Charm?) Weeeeeelll - apparently, an "undocumented feature" of those two
songs is a slight magic resistance debuff.

Guardian Rhythms only purpose is in twisting multiple songs in the Rhythms
lines, and ONLY if you are already twisting the other two. It gives the
same AC and MR bonus as Purifying and Elemental, but without anything else.

Psalm of Vitality appears to have a slight disease-removal effect. Purity
seems to remove poison, and

Fufil's Curtailing Chant only does 1/4th the damage of the Discord, but it
DOES have a better MR Debuff.

Psalm of Warmth gives Infravision, Cooling gives Ultravision.

Denon's Dissension is a mana-debuff, but since NPC's don't USE mana, it's
utterly useless.

Tuyen's Chant of Flame/Frost supplements it's weak damage by adding a
Fire/Cold resistance debuff (So theoretically, they'll take more damage if
they resist less? Stick with Denon's.)

Syvelian's is exactly the same as Alenia's as far as the data file is
concerned (except for the material component in Alenia's)

Mystic Shielding seems to have an unknown effect, as well as a DoT
effect. How strange.

Niv's, from the looks of the effects will add a rune-like coat of
protection, as well as healing, AND giving you an HP buff AND a decent STR
buff. Wow!! Nice song (if it works...)

Chord's of Cessation adds a damage effect to it's slow-down, however, it's
slow-down is no more powerful than the Chains. If anything, it's worse
than chains, because while they both slow down attacks, only chains slows
movement.

And man - I can't wait for Verses of Victory (level 50) That is one SWEET
song ;)

All information comes from the spdat.eff and/or spells.eff files,
reliability subject to Verant's programming abilities.

Talies the Researcher