Hello Eledan, let's make your dude frigging awesome.
Suggested PrCs
War Mage: Found in Dragonlance splat this 5/5 casting PrC grants your nearby allies Cha-to-AC. The gem is ConMod/day you get +3 per die to damage. The ConMod nerf is located in another splat, source unknown.
Stormcaster: Found in Stormwreck this 4/5 casting PrC has one of the most amazing 5th level Class Features ever made; Thunderbolt. Every Electricity-dealing Spell additionally deals Sonic damage and has a Fort-vs-Stun effect potentially turning every blasting Spell you sling into a crowd controlling effect. You lose a CL for this abuse through, still worth it.
Incantatrix: The second runner up due to being able to aftermarket Metamagic. You know about it so enough said.
Spelldancer: If the Incantatrix is on the table then ask about this one, a single level dip pays for your daily Persisted Spells.
Prestigious Bard: Found in Unearthed Arcana this 0/1 casting PrC grants the entire Bard List to your Warmage which has some very amazing Spells like Emperal Ecstasy, Snowsong, Glibness, etc.
Suggested Feats
Snowcast + Frozen Magic + Cold Spell Specialization + Draconic Aura + Ice Armor(item): If it's cold outside you can grab a handful of snow to increase the CL of your Spell by +2, the Save DC by +6, and add +2 per die to damage. Getting a Cleric to cast Cold Snap (and possible control weather) ensures this happens and you get another +1 per die to damage. Downside, spamming winter in the local environment tends to piss the natives off. See Frozen.
Iron Will + Reserves of Strength: +3 to CL and allowance to break CL caps. Currently unknown if your supposed to totally break cap or just by the abused amount (sic 15th level gets 18d6 Fireball or 13d6?) so talk to your DM.
Energy Substitution + Energy Admixture + Acid Sheath(Spell): Acid Sheath works kind of like Fire Shield in that anyone hitting you takes a bit of Acid damage, it's biggest trait is it also grants +1 per die to acid damage.
Pyro + Fiery Spell + Caustic Mire(spell): Up to +3 damage per die with Fire-based Spells. Due to the wording Pyro does not piggyback like Snowcast Energy Admixture Acid Sheath via War Mage does (which btw is +6/die).
Suggested Items
Ring of Mystic Fire and/or Ring of Mystic Lightning: Another one of those MiC charges-per-day item, on max expenditure it further adds +4d6 to the respective Spell. Talk with your DM about a differant Energy Type if if Electricity/Fire is not your desire.
Suggested Spells
Wreath of Flames: This Persistable Spell deals 2d6/rnd to any opponent near by and also adds +2d6 to your melee attacks. Add Energy Admixture & a Ring of Mystic Fire for abusive numbers that'd replace a request for a Dragonfire Bard.
Fire Shield: And it's extended family Holy Fire Shield (1/2 holy), Radiant Shield (electricity), Cacophonic Shield (sonic, deafens), Sonic Shield (sonic, pushes away), and Spark Shield (electricity, deals a tad less but if they are wearing metal then a tad more). Again a Ring of Mystic X & Persist is the way to go. You can potentially stack them as well, Spark, Holy Fire, and Fire(cold) for 1/2 from three types of Energy and everyone hitting you dies. Like too many dice to roll so the DM just throws the statsheet into the garbage and says he's using ranged creatures from now on.
Charisma Optimization
Sure you have Int-to-damage but you know what hampers a Spell's damage more than your Int? Successful Reflex Saves.
* Wand of Righteous Aura: +4 Sacred to Cha.
* Runestaff with Devil's Ego: +4 Profane to Cha.
* Said Runestaff also has Nixie's Grace (or PrC Bard it): +8 enhancement to Cha.
* Ditto for Snowsong: +4 Moral to Cha *unpersistable*
* And talk to your DM about Horse Shoes of Flame. It's reasonable that with a successful UMD Check, consuming your Hand & Boot slots, you can activate the items for a +10 Bonus to Int and a +6 Bonus to Cha. Someone *cough* Ols *cough* ruled it in but it turned you into a horse in his game. Just use Alter Shape, or a Racially-granted Shapechange like I did, to reshape out. Where there is a will there is a way so long as it's not a no.
How you put the pieces together is of course up to you. Good luck.