I think Bards are great - and I have two players who play Bards almost exclusively - because they are what they need to be, when you need them to.
For example - at the beginning of most battles, a bard would usually slap a Haste spell on the party - freeing up the Arcane casters at the beginning, where a well placed spell could do a lot of damage. During the middle stages, they would support the party with physical attacks and bard song. If several party members were injured, they would step in and heal the one with lesser wounds, freeing up the cleric. If there was a less-important enemy to check, the bard would fill in for the fighter.
Perhaps it's just because of my DMing style, but I find that Mages make their biggest contributions earlier in combat, when they unleash their powerful spells, and tend to fade towards the end of the encounter (or the day), when their higher level slots are exhausted, or they wish to save them for the next encounter. Fighters, on the other hand, do better later on as they are mopping up weaken foes, all day long. Clerics can contribute offensively earlier in combats, but in later rounds are more restricted to healing wounds. Rogues, monks, and other specialized combat classes have situational contributions.
But even excluding the +1 bonuses on the Bard Song, bards make the party a lot more efficient by freeing up other party members - in combat, on the fly. Buffing the party helps the Wizard throw that first Fireball. Tripping the beasts helps keep the meleer's safe and deal their damage, when combat is tight and heavy. Healing the slightly singed but less threatened Wizard leaves the cleric to Heal the fighter's lost 98 hit points, while keeping both characters safe.
And that bard song does really add up : )