This is just a list of some of the bardic prestige classes available. It is by no means exhaustive, and your character might not be ready to qualify for some of them. (Not to mention the fact that not all these prestige classes' flavour might suit your halfling character.)
As Steven already mentioned above, in Complete Arcane you can find both the Seeker of the Song and the Sublime Chord prestige classes. The latter prestige class gradually moves into the wizard/sorcerer spell list for spell levels 4 through 9 (it opens up the possibility from spell level 4, and is the only game in town for spell levels 7 to 9).
In Complete Adventurer you can find both the Fochlucan Lyrist and the Virtuoso. The F. Lyrist is the closest that one can get to the old 1e Bard, and I believe that one can qualify as Bard 7 / Rogue 2 / Druid 1. The Virtuoso is a more traditional bardic prestige class.
In Complete Mage you can find the Lyric Thaumaturge.
In Complete Warrior you can find the War Chanter.
In Complete Divine you can find the Evangelist.
There are other possible prestige classes in Complete Scoundrel, but none specifically aimed at Bards (IIRC).
Frostburn has the Stormsinger prestige class.
The Draconomicon has the Dragonsong Lyrist.
If the character in question somehow becomes a spellscale, there are three spellscale bard substitution levels (1, 3, 6) in Races of the Dragon.
Libris Mortis has the Dirgesinger prestige class (non-Good).
Depending upon the campaign setting, other sources might also be available.