For my part most of my E6 builds are theoretical. At least until my current character bites it. Our party is mostly made up of Martial characters and except for the lack of out of combat healing has been doing really well in our Greek themed game. Think the Adventures of Hercules turned into a campaign. Surprisingly our Solitary Hunter Ranger has been the best at all around usefulness both in and out of combat so far.
With builds I've found that it doesn't take much optimization for martial characters to compete, whereas casters, because of their early level physical frailness, need some help.
I'm currently playing Harphus a Crossbow sniper that has been kicking all kinds of ass even without using the Aptitude enchantment that was the initial inspiration for the build. I want to eventually be adding Lightning Mace, Boomerang Daze, close combat shot from Versatile Combatant, and size increases from the unarmed strike boosts to his crossbow attacks. He designed and built a repeating Great Crossbow for use in this and has been using his unarmed strikes to fight in melee as needed. He's been a lot of fun.
Exoticist Hit & Run Fighter 1 / Martial Monk 2 (DM house rule gives Monks full BAB and 6 skill points a level, reduced to 5 for Martial Monk) / Warblade 2 / Crusader 1
Feats: Combat Reflexes, WF: Light Mace, Two Weapon Fighting, Strange Strike (ExF), Versatile Unarmed Fighting, Improved Critical Great Crossbow (MM), Superior Unarmed Strike, Stone Power, EWP: Hand Crossbow, EWP: Great Crossbow, EWP: Spiked Chain, EWP: Xendrik Boomerang
He can fight ranged and melee with equal skill and can sacrifice accuracy for toughness using Stone Power to tank when it becomes necessary.