Okay...got some time to type up a post.
Heres a rundown of all the bardic abilities that ive seen and used:
Warrior/Rogue Abilities: They get a basic warrior and thief abilities, but nothing spectacular. Missing the prime abilities that makes a Warrior a tank, and of course cant stab/circle, the key aspects of a rogue. Some useful stuff though (pick locks, sneak, protect, rescue, kick/bash)
Mage Spells: Bards get basic mage spells, but about 8 levels after a mage would get them. While this might help a little, it really limits the effectiveness it overall provides, getting magic missiles at 9th level isn't going to help much against the mobs you'll be hitting. Something like just using fireballs at 40th, nothing much to brag about, comparatively, but it might see use.
Wealth and Glory: Pretty cool song, in my opinion, though limited in use. If you know the area a item or book pops in, it might help single it out to find, but not effective really in finding new equipment (as you need to know the name of the item to sing about it).
Brother In Arms: Semi-effective at lower levels, adding +1 to Hit for everyone effective. But just as lower level mage spells become obsolete as you adance in levels, so does this song. No Lvl 40 bard is going to waste their time singing this song, when they could use other classes abilities (if not singing some other more effective song.
Beyond the Shadows: Haven't used this at all, because Tetsu has the much more effective Sense Life and Perception. I suppose it might be semi-usful if you have nothing else to detect hidden mobs.
Sanctuary of the Soul: Truthfully this SOUNDS like a great song, if it ever worked. I've tested it and NEVER seen it stop a mob from casting/proccing, even with a +12 Charisma [supposedly +15 is the best], the littlest of mobs still cast/proc.
March of Heros: Not that effiecent, but nifty in some situations. About the only time it ever sees use for me is when doing scatter quests
Fare thee Well: Really haven't seen any effect to this either. Not sure if this spell just gives bonuses to saving throughs against spells/procs, but haven't really seen an effect. Having it unusable in combat (stops if you get hit), makes it all the more useless, if it does work, since you'll get hit by a proc and the song stopped.
Dreams of the Castle: Highly effective song, use it constantly. Bonus to regen is always appreciated in a group. Not sure how the bonus is calcutated, I thought it was constant, but Tetsu only gives +9, while Taliesin gives +10.
Dance of the many: I've never used it. Suppose against Mobs with Fear it MIGHT be useful, but I've never come across a need.
Hymn of the Morning Star: Not that effective, whoppie, you can wake people up. The only use I've ever used it for is draggin Pthieves out of no-cast rooms to web them (Make them wake so they can be pushed).
Sacred Reprieve: Not very useful, though its had its moments. Very risky to use against big aggro's though.
Haunted Dirge: Haven't really had a chance to use this yet, so not sure how good it is. I suppose it might be helpful to for mobs to flee, but i have my doubts.
Flames at Midnight: Fairly effective Blast spell, comparative to a Mass Ice Ray in damage, with several additional effects (increased AC of target, Additional damage to subsequence ICE spells, etc.) Not bad, least until you get cry.
Gods of War: Most used song, and highly effective. +10 damage for every target, for a bard prime. Very good!
Reign of Confusion: Haven't really used this either, so not sure what confusion does, or how effective it might be.
Eye of the Beholder: Okay in some situations, but untargetable, so hard to use if theres multiple mobs in the area.
Rina Cruinne: No one complains about a better chance of a Raise succeeding
Cry of the Avatar: Highly effective blast ability. Tested to do about 210ish damage if save isn't made, with a high charisma can almost be as effective as a Mass Firestorm (except for the avatar bonus to firewind).
Dance of the Seven Luck Gods: The Bards ONLY Prime ability (save for bonuses to a few other songs, Dreams and Gods mostly). Seems like it will be very cool, but is pretty expensive, and unwieldly to use effectively in any manner of group. (100 mana initial expense, +100mana/tick waiting for the mob to pop). Still, double the pop chance is really good, so think it will always be good.