I play support Sona with a lot of mana hungry ad carries. With the extra mana regen at the beginning the ad carry can spam their abilities to secure kills to help with their late game. This is only my first build, and I will be updating it. I do not have this build explained very much (that will happen soon), but I hope you can love this as much as I do.

Pros

great for mana hungry ad carries
great support
great heals and buffs
does damage for pressure

Cons

only mana to help the adc is from (mana manipulator / soul shroud)
no slow / stun that isn't her ult

Power Chord: After casting 3 spells, Sona's next attack deals 8 + (10 x level) extra magic damage. This enhanced attack has an additional effect depending on which spell was cast last.

Additionally, Sona's auras persist for 1 seconds after deactivating. Sona's basic abilities also set off a .5 second cooldown to the other two basic abilties.
(btw, power chord can crit, and applies any on-hit effects as well.)

Hymn of Valor: Sona plays the Hymn of Valor, granting nearby allied champions 4 / 8 / 12 / 16 / 20 bonus Damage and Ability Power. Additionally, casting this ability sends out bolts of sound, dealing 50 / 100 / 150 / 200 / 250 (+70% of ability power) magic damage to the nearest two enemy champions or monsters.

If this spell was last cast when Sona's Power Chord is ready, her next attack will dodouble the damage of her Power Chord.

Aria of Perseverance: Sona plays the Aria of Perseverance, granting nearby allied champions 3 / 6 / 9 / 12 / 15 bonus Armor and Magic Resist. Casting this ability sends out healing melodies, healing Sona and a nearby wounded ally for 40 / 60 / 80 / 100 / 120 (+25% of ability power). Additionally, both Sona and the healed champion will have the bonuses of this aura doubled for 3 seconds.

If this spell was last cast when Sona's Power Chord is ready, her next attack will de-buff the target to deal 20% less damage for 4 seconds.


Song of Celerity: Sona plays the Song of Celerity, granting nearby allied champions 4 / 8 / 12 / 16 / 20 bonus Movement Speed. Additionally, casting this ability energizes nearby allies 6 / 8 / 10 / 12 / 14% additional movement speed for 1.5 seconds.

If this spell was last cast when Sona's Power Chord is ready, her next attack will slow the target by 40% for 2 seconds.


Crescendo: Sona plays her ultimate chord, forcing enemy champions to dance (stun) for 1.5 seconds and take 150 / 250 / 350 (+80% of ability power) magic damage.