The trick on the bard that most people seem to overlook is that to be rather badass, don't try to focus on doing some other classes' job - focus on your barding.
Song of the Heart feat (+1 to just about everything bardic music. Inspire Courage goes up by +1, Inspire Comp is now +3 instead of +2, Inspire Greatness now grants 3hd instead of 2, etc). Particularly of note is Inspire Greatness - those hit dice are ablative and benefit from the target's con mod. And at 15th level you'll have up to 15 uses of it per day...
Inspirational Boost spell. A 1st level swift bard spell that slaps another +1 on to your Inspire Courage. Inspire Courage is like voltron - the more you pile on the better it gets.
Lyric Spell feat. Lets you trade in bardic music uses per day for a spell. Extra mojo on demand is ver' nice.
Extra Music feat. +4 additional music per day each time you take the feat. Then take into account Lyric Spell and Inspire Greatness and you can see where this is going.
Lingering Notes. Your music now lasts for 10 rounds after you stop singing instead of the regular 5. Very useful. Frees you up to do other things without having to worry about re-musicing right away.
Fascinate/Suggestion. If you're out of combat, people are your plaything. The will save DC is your perform check result for god's sake. Nobody's going to make that. We're talking 30s-40s without even trying.
For your spells, look at healing, enhancing spells (haste is a cherry, for example), and enfeebling spells (slow, dominate person, dispel magic, modify memory, etc - bestow curse was a personal fave until they took it off the bard list in 3.5).
Oh, and you have free whip prof. Don't forget that. Can come in handy.
Bards may only have 3/4ths BAB, but give 'em a few seconds humming When Johnny Comes Marching Home and all of a sudden he's gone from +11 to +19 BAB (not to mention 3d10 extra HD, a bonus to saves, and +5 damage) at 15th level. Base. Before stat mods and the like. Scoff not.