I see a lot of suggestions to make the fighters have different styles. If the players are close friends and the characters are too, why not have them be very similar and take advantage of all those Teamwork Feats that require at least two people to unlock some really neat group tactics effects. I play a 6'2" Human two-weapon fighter(not the archetype, bleh) that frequently teams mobs with my wife's 2'3" Halfling (I know really small, DM allowed it due to character back story). I take a hit or two sometimes so that she is in position to knock them down. If she doesn't, the Teamwork feat: Precise Strike gives me an additional 1d6 (plus a slew of other goodies from various magic items that can allow me several more hits than my 'normal' full attack at my level) and she most definitely mops it up with Precise Strike adding to her sneak attack.
To be fair, we are in a campaign with several brand new, very unimaginative players. The wizard is stuck on using his wand of Magic Missile at 11th level because "Its the only thing that always hits with out frying you guys!" The ranger forgets he has a wolf sitting at his heels, despite my pack of war dogs, one of whom doubles as the halfling's vicious mount, and seems to forget he can shoot things from far off, even in melee, thanks to those feats he asked for advice about. The cleric sadly forgets all about trying to heal or cast virtually any spell (until recently when the first action has become 'bless' followed by Spiritual Weapon). We actually have a second fighter whose style is very different from my own (big honking two-handed sword you got there), but has started getting with the program with Gang Up Feat. He enjoys the bonus and the big bads go down fast under melee assaults. Improved initiative on our part helps too: The bad guy generally takes a dirt nap by the third round, if he lasts through the first.
I'm wondering if anybody out there has gone through the effort of really building up combat teams (melee, caster, or mixed) just to see what kind of gank squad can really be pulled together. Stealth Synergy alone makes for one heck of a secret police squad when the point man is a stealthy rogue and every member has taken the feat that basically allows him to do the check for everyone in the group that can be seen.