I want each character in the party to buff the party, so that they are significantly better together than apart. Even some teamwork feats might be a good call. I know the Cavalier and Bard are just designed for this. But, I also think that the Paladin, Cleric and Ranger could be good classes. So, give me some ideas and build suggestions.
basic group build for cookie cutter grp:
tank: fighter or paladin
healer: cleric or paladin
burst dps: rogue, ranger, or sorcerer/wizard
utility/battlefield controller: bard/summoner
the problem with what you want to do is that the cookie cutter is pretty much based on the "needing each other" concept already. by asking your players to all be utility classes you are gimping other cerucial aspects of the group as a whole. thinks like a damage sponge tank or a massive dps class end up falling away and you end up with a grp who either doesnt take much damage or doesnt deal much damage...
even if you go with a paladin,cleric, sorcerer, bard group (basic cookie cutter) if you ask them to ALL focus on buffs then the paladin is no longer a tank and the sorcerer is not a massive dps.
instead i would suggest having each PC play a specific ROLE which the grp cannot be without such as tank, healer, dps, and support...
You have a theme, but I've always thought two Bards could coexist easily in a party.
Mr. Party, and Mr. Pooper. Tigger and Eeyore. One buffs your party, the other debuffs the opposition.
Two bards with diametrically opposed personalities and builds forever fated to travel together.
Plus they make a lot of noise.
I'm trying to figure out how the synergy would work. Okay, so let's say around level 7-10, you'd have:
The main buffer:
A bard who can Inspire Courage for +2 to atk/dmg/saves as a move action, then cast Good Hope for a +2 to atk/dmg/saves (stacks with IC) as a standard action.
The battlefield controller:
A divination wizard who can cast Haste as a standard action (which means he can't cast some battlefield control spell that round, which could be bad).
The utility leader:
A cleric who would cast...? Maybe Prayer or Blessing of Fervor, or perhaps use an aura ability that could buff the party.
The damage dealer:
A paladin who would do.... something? Or maybe a Cavalier?
The wizard would definitely be better off using a control spell, which should be fine, because the cleric can cast Blessing of Fervor to give the attackers the extra attack they need. Not sure what the damage dealer can do to help with the buffing.
Be careful in the Bard and Cavalier mixing. Some of those bonuses overlap. Order of the Dragon is probably the best for overlap as the abilities granted are unusual and hard to come by with other sources.
Teamwork feats get silly in later levels.
The Honor Guard archetype is even more buff friendly (changing out most of the selfish charge abilities for team-friendly class features), and pairs exceptionally well with Order of the Dragon.
In a party my friends are in (but I'm not as I work that day), the wizard is a Divination wizard, you know, the ones that always go first. They all have the lookout feat and they stay in close proximity.
Divination is not a bad wizard strain for a buffer in that going first or knowing what's coming lets you cast better buffs. That said, Transmutation gets all the groovy ones.
I wonder if a Witch wouldn't be a good addition. Hexes are POWERFUL buffers as they are debuffers. A witch focused on cackling up the good hexes makes your main damage dealer an unstoppable juggernaut.
Some pieces are easy.
Evangelist Cleric (competence to attack and damage)
Order of the Dragon Cavalier (circumstance to attack and damage against challenge)
Freebooter Ranger (untyped to attack and damage against target)
For the fourth slot I'd just put a wizard for the spell list. Someone's got to cast fly and teleport and all the game changing spells that high level play assumes.
Inspiring Commander Order of the Dragon cavalier, Archivist bard, Wizard/Sorcerer, something that sticks pointy things in the enemies.
Cavalier inspires courage as a bard providing competence bonuses to attack and damage then uses aid another on teammates, archivist bard can easily pass monster knowledge checks providing insight bonuses to attack and ac and has spells to further augment allies (as well as heals). Wizard/Sorcerer controls the battlefield while the last member of the team cuts everything down to size due to massive bonuses.
I like buff focused parties myself, but the problem is you are better off having at least one character that makes best use of being buffed. A barbarian with the focus on taking large weapons and attempting to pass them through the enemies bodies is a good choice to be buffed. Essentially the party becomes rage delivery systems.