I was making some new ideas/abilities for the 3e Bard a few years back, so if you want I have a list of ideas I had been tossing around.
~ Combat Aid ~
Inspiration: Gives allies combat bonuses (AC, Attack, hitpoints). I had temporary hitpoints in this, but in 4e I could see it being straight up healing.
Battlechant: Gives allies damage bonuses (either Str boost, or specific damage riders).
Accelerando: Speed or Haste-like effects.
Vibrato: Bard's weapon takes on additional sonic effect/damage.
~ Attack ~
Bellow: Yells that do sonic damage to the enemy. Rider effects for additional abilities include: Stun, Deafen/Lower AC/Combat Advantage, Sicken/Nauseate/Unconscious, Fear, Dispel Magic effect.
Daze: Kind of a hypnotizing effect. Additional abilities tied to this one would be: Charm, Sleep, Confuse, Dominate (as per 3e type effect).
Despair: Demoralize the enemy. Additional rider effect abilities would add Slow (less attacks) or reduced Speed.
~ General ~
Fascinate: Hypnotize out of combat, with later abilities including: Suggestion effects, Mind trickery, Geas/Quest power.
Blur: Make yourself or someone hard to see/strike. Miss chance type effect.
Healing: Provide general healing and curing (removing poison/disease).
Resistances: Reduce damage done from the elements.
Disguise: Fool others into thinking that you, or others with you, look like something else.
The idea was based on Spell the 3e Bard got, and removed spellcasting in the general sense from the class. These were the most appropriate effects the Bard should retain.
I've always felt that the Bard in an adventuring capacity was meant to be sort of like how Battles in the past would have Warpipes or Drums to urge their fellows on, and demoralize the enemies.
One aspect that I hadn't considered, but could make sense historically and would fit the game, is to use Music or Instruments as forms of Combat Communication.
Essentially, since everyone is using the Bard's cues to better organize their attacks and movements, you could give the Bard some Warlord style abilities of generating movement or attacks for others.