For possible class combinations Bard/Sorcerer is standard Core and allows you to use your 2 free books and single homebrew option on something else.
If you are looking for versitility then I would highly suggest Factotum from Dungeonscape. Since it is gestalt I would almost require that you do not PrC out of Factotum.
The sheer ammount of versitility gained from Factotum alone will give you a huge ammount of flexibility, both in spells and in skills. Plus the ability to add your Factotum level to any trained skilled 1/day per skill will help net you crazy political powers. (Diplomacy, Intimidate, Bluff, ect....)
Bard 20 || Factotum 20 is simple and standard. But we can do so much more.....
Using Dungeonscape & Races of Destiny as your two alotted books gives us.....
Bard 5/Chameleon 10/Bard 5 || Factotum 20
* High number of skill points and ALL skills as class skills.
* Ability to cast up to 6th level Arcane spells from ANY list.
* Ability to cast up to 6th level Divine spells from ANY list!
* Ability to cast up to 8 arcane spells of 7th level or lower as SLA's & you can switch the chosen spells out every day. (Also SLA's ignore material components which opens up sooo many doors.)
* A floating bonus feat that you can change every day.
* Capability to add +6 to two stats each day.
* Cunning Brilliance (If you get this far you now get to gloat and steal any EX class ability you want for 1 min/day.)
Another option that focuses more on your Bardic aspect is by using the Complete Arcane & Complete Mage.
Bard 5/Lyric Thaumaturge 5/Sublime Chord 10 || Warlock 20
* 24 hour self buffs from Warlock reduce your need for certain utility spells.
* Warlock gives you some damage dealing capabilities as well as several useful utility funcitons. (The level 12 ability can make you a lot of money if you know how to "offer" your unique services.)
* Beguiling Influence (+6 unamed bonus to Diplomacy/Intimidate/Bluff)
* 10th level Bardic casting thanks to Lyric Thaumaturge.
* Essentially you only need 2 major attributes. Charisma/Intelligence.
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* 4th-9th level spells thanks to Sublime Chord