E6 PrC+ HandbookMany of the same tips provided by Nytemare3701’s handbook apply, but I will expand on that material, as well as options that are more applicable to E6 PrC+
Races, Templates & AgingE6 reduces Level Adjustment via the Point Buy table. As such, some races & templates are quite optimal if reaching for min/max ability score arrays. An LA+1 race or template with a net +4 in primary ability scores begins to contend with a 32pt (LA+0) vs 25pt (LA+1) buy, depending on how min/max and SAD/MAD your build is.
Aasimar, Zenythri & Planetouched in general
Catfolk
Chaos Gnome
Draconic Template
Lloth-Touched, makes Drow somewhat salvageable
Player Race List with LA +1 and LA +2
http://www.minmaxboards.com/index.php?topic=342.msg1537Master Template List
http://community.wizards.com/go/thread/view/75882/19869266/Master_Template_ListSavage Progressions/Template ClassesE6 can support a character choosing to take a Savage Progression Template Class in general.
E6 can also support a character choosing to be a partial Savage Progression Template Class at character creation. For example, a Tiefling (LA+1, point buy 25) could choose to be a 1/4-Fiend by taking 2 of 4 of the levels of the Savage Progression Template Class at character creation (LA+3, point buy 10)
Ultimate this is up to the DM, since things like the Savage Progression Ghost Template exist within this sphere.
AgingDo not overlook the Middle-Aged Category
At middle age, -1 to Str, Dex, and Con; +1 to Int, Wis, and Cha.
With only +1 Ability Score increase in the lifetime of an E6 character, the middle-aged category can easily help smooth out ability scores to even values.
FeatsSudden Empower: Damage amp for classes that otherwise don't have easy metamagic adjustment
Elder Giant Magic: Useful to raise CL for long duration buffs
Reserves of Strength: Still useful for breaking caps of lower level spells. Getting the most of every level of spell is desirable with Recharge Magic.
Dwarf's Toughness: Better than Toughness for characters with good fortitude save. Can be taken multiple times.
Uncanny Forethought: Great way for Wizards to have utility spells available spontaneously. Note that it doesn't really open up any sort of super buffing abuse, as there is not much in the way of general recharge buff spells.
Ocular Spell: Can save some time on a recharge by preparing ahead of time, as the spell is cast and then held in the eyes.
1st Level Only
Arcane Schooling: Opens up a wide variety of spell trigger items for classes with limited spell lists, without resorting to level dipping or use magic device.
Dauntless: +5HP is better than Toughness, if additional HP is desired
Mind Over Body: More efficient HP gains if you're planning on metamgic
Spellcasting Prodigy: Efficient way to gain additional spell slots and boost DC
Furious Charge: +4 ATK on charge, reasonable for charger builds
Otherworldly: Outsider Type
Bloodline of Fire: +2 CL on [fire]
Militia: All Martial Weapons proficiency
Luck of Heroes: Luck Bonus +1 Saves, +1 AC
Hidden Talent: 2PP + 1st level power
Initiate of X: Various spells & skills added to list
ItemsMetamagic Rods: Note that they need to be crafted at lower than the default caster level of 17th. "While item creation costs are handled in detail below, note that normally the two primary factors are the caster level of the creator and the level of the spell or spells put into the item. A creator can create an item at a lower caster level than her own, but never lower than the minimum level needed to cast the needed spell. Using metamagic feats, a caster can place spells in items at a higher level than normal. "
Quori Embedded Shard: Power Link: Raise augment capability
CombosKobold Sorcerer 1 + 4/5 PrC + Greater Draconic Rite of Passage = 3rd level spells
CL Boosters for damage types
Any: Spell Thematics (+1 CL),
Fire: Bloodline of fire (+2 CL), Calishite Elementalist: Fire (+1 CL), Elemental Spellcasting (+1 CL), Fiery Burst (+1 CL)
Air: Calishite Elementalist: Air (+1 CL), Elemental Spellcasting (+1 CL), Hurricane Breath (+1 CL)
Water: Elemental Spellcasting (+1 CL), Aquatic Breath (+1 CL)
Earth: Elemental Spellcasting (+1 CL), Clutch of Earth (+1 CL)
Acid: Acidic Splattter (+1 CL)
Force: Blade of Force (+1 CL), Invisible Needle (+1 CL), Holy Warrior (+1 CL)
Sonic: Clap of Thunder (+1 CL)
Electricity: Storm Bolt (+1 CL)