Just some ideas for the various classes to, in some cases, make it more reasonable to take pure levels in a class, though the aim is to balance it so that splashing classes isn't "worse".

Idea 1: Bard "Skald" capstone.

Warrior-Skald: Though you are a poet at heart, you have also firmly established yourself as a warrior. Your Inspire Courage song now granted full BAB to you and all around you, and you gain +2 Con. If a character already has full BAB, they instead gain an additional +1 to damage and attack.

Idea 2: Ranger "Melee" capstone.

Jungle Beast: You are as a jaguar, swiftly pouncing upon your foes and tearing them to shreds with your weapons. Your attack speed increases by 20% (stacking) and you gain +2 to strength.

Idea 3: Cleric "Offensive" capstone

Holy Avenger: You are no mere healer, delivering swift retribution to your enemies. You gain +2 Wis and 20% additional effectiveness to your damage spells.

Idea 4: Sorcerer "Control" capstone.

Manipulator: While others blast and smash their way through obstacles, you are a cunning individual who prefers to manipulate your adversary. You gain +10 to spell penetration, +2 Cha, and the duration of your control spells is doubled as if Extend were applied.

(Basically, the idea behind this is for the Sorcerer to be a viable CC candidate without intruding in the wizard's territory)

Idea 5: Wizard "Offensive" capstone

Elemental Genius: You have gained an intricate understanding of the elements, far beyond that of any ordinary wizard. You pierce enemy resistance by 50%, and enemies who absorb an element will no longer absorb it.

Idea 6: Paladin "Support" capstone (Because everyone needs at least one capstone that people wouldn't ordinarily take, amirite?)

Healing Hands: Though you are a warrior, the touch that the gods have gifted you with is full of immense healing. Your "Lay On Hands" spell now targets in an area around your target, healing others for half of the target's healing. You also gain +2 to cha.

I figure if I throw ideas out, eventually I'll throw out a good idea and maybe it'll be used. On the other hand, I also hope they ignore any bad ideas I may have accidentally thrown out.