Since in 4e, Bards have Otherworldly patrons I would like to see them work something like this:
This is if his powers are based off the control and manipulation of emotion.
The Otherworldly patrons would be beings beyond the gods, who feed and play with the emotions of mortal creatures; a tingle of fear down your spine, a flush of excitement from a thought, that is the work of these beings.
A Bard is someone who has gained the interest of these patrons by heightening and enhancing the emotions of others through his/her art. As such the patron that discovers the Bard begins to allow him to manipulate, the certain emotions that patron resides over and has a taste for.
So almost like a Warlock with pacts, the player chooses which patron took a interest in them (obviously related to whatever background the character has) and gains powers based around that patron's dominant emotion. Be it; fear, joy, sadness, anger, etc.
The Bard would have some basic control over other emotions, but the patron's dominant emotion be the most easily manipulated/controlled.
Now through their own research and lore-study and what has been given to them through the patron. A Bard learns much about mortal lore, for it is through tales and legends we truly see the effects of emotions and feelings on mortal beings.
I expect power-wise, a Bard would have lots of controlling spells (based off manipulating emotions), illusion (cast images inside people's minds by provoking their emotional state) and some basic social and physical attributes to showcase the Bard's life prior to being discovered by the patron.