Born of the Three Thunders - understanding the feat

[NoACWarrior]

I'd like to take Born of the Three Thunders when my sorcerer hits level 6.

Plead your DM for dragonlance spells since its one of the better options at level 6 for both AoE and damage. Otherwise your only AoE option is Ice dagger which does horrible damage. Other spells you could take a 6th level just don't have the multi targeting above 1 or 2 targets yet and are kind of ineffective for what you are trying to do (entire enemy target lockdown). I again emphasize the utility of mult targeting spells over AoE - they will allow you to make much better battlefield effects and not do friendly fire (except in the case of Palin's Pyre which is pretty much the best to use short of the higher level spells).

As for specific spells for you to take at level 6 -
Palin's Pyre (Dragonlance, Fire 3) - 5ft squares AoE (1 per CL), reflex partial (still damages)
Ice Dagger (SpC, Cold 1) - single target but 5ft AoE around target for 1 damage, no save

Spells you qualify for but probably shouldn't take at level 6 but could later - (you get only 2 targets at 6)
Ice Darts (Frostburn, Cold 2) - multiple targets (+1 per 2CL over 3rd max 5), no save and no SR
Elemental Dart (Dragonlance, Any 2) - multiple targets (+1 per 2CL over 3rd max 5), fort half
Shocking Spark (Dragonlance, Electricity 2) - multiple targets (sort of up to 3), no save

Spells you qualify for but probably shouldn't take at level 6 but could later - (you get only 1 target at 6)
Hailstones (SpC, Cold 3) - multiple targets (1 per 5CL), no save and no SR
Scorching Ray (PHB, Fire 2) - multiple targets (+1 per 4CL over 3rd max 3), no save

Spells you could take at the appropriate levels -
Deadly Sunstroke (CMag, Fire 9) - multiple targets (1 per CL), fort half
Scalding Touch (MoE, Fire 7) - multiple targets (touch 1 per CL), fort partial (still damages)
Entomb (Frostburn, Cold 6) - multiple targets (1 per CL), fort partial (still damages)
Moonbow (SpC, Electricity 5) - 3 targets, no save
Dalamar's Lightning Lance (Dragonlance, Electricity 4) - multiple targets (1 per 5CL), fort half
Burst of Glacial Wrath (DragMagic, Cold 9) - 30ft cone AoE, fort half
Channeled Sound Burst (CMag, Sonic 5) - cone length depends on action AoE, fort half
Earth Reaver (SpC, Fire 5) - 20ft spread AoE, reflex partial (still damages)
Shrieking Blast (HoB, Sonic 5) - 40ft radius burst, fort half
Shout (PHB, Sonic 4) - 30ft cone AoE, fort half
Parboil (Sand, Fire 4) - 20ft radius spread AoE, fort half
Detonate (PHBII, Fire 9) - single target (but AoE if fails fort save or dies), fort partial (if dies get AoE)