5th and sixth members

[Emperor Demonking]

Presuming the default party of fighter, cleric, wizard, rogue. What do you want in a fifth or sixth party role?

5th, a buffer or support role. This is often done by bards but can be done with clerics or wizards.

6th, a flank buddy who can do something the others can't. A monk can do this or yet another wizard.

[Rachel Lorelei]

I want someone who can contribute as much as any of the others, even if it's by helping the others contribute.

Dragonfire Adepts, with their battlefield control/debuffing, make good "extra" party members. A sorcerer does, too, since his narrowness of options is less important with a wizard already in the group. A divine spellcaster can provide mass buffing and healing.

[Orzel]

A ranger and another wizard
or
a druid and a bard

for some buffs, control, damage, and nature skills.

[Proven_Paradox]

When you've got that many characters in your group already, there's room to experiement and try new things with the other slots. Gish builds can be a lot of fun, and if all the bases are covered then they can work to compliment what's there by providing basic spell support and some melee assistance at the same time.

A crafter is always fun, too. Artificers and such are always appreciated if the other roles are filled.

When you've got that many people, there's likely to be more monsters coming at you, so another fighter-type character might be appreciated, since one person might not be enough to keep the casters covered.

[squishycube]

What I like to do in parties larger than 4 is swap out the default roles associated with the stereotypes.
What I mean is that in a party of four there are 4 stereotypes, each of which have certain functions. The rogue has lots of skills and makes a good secondary combatant, with sneak attack. In a party of five, a fighter with sneak progression could take the sneak part of the rogue and leave the skill monkey part to, for example, a bard.
In a party of four you will very quickly get the four default stereotypes to fill the default roles.

[Talic]

Depends on the campaign. Generally, I prefer a 2nd rogue. I find rogues work well in tandem, and trapfinding backup is a great skill to be redundant in.

In heavy undead campaigns, I prefer a second fighter type, usually, maybe another cleric.

If the extra is a wizard, I prefer the uber-specialist, with a narrow field.

[cupkeyk]

1 Batman
2 Heal Bot
3 Skill Monkey
4 Tank
5 Face
6 Archer

[Gardakan]

In a group of six we need...

2 healers
2 tankers/dealers of damage
1 spellcaster(wizard, Sorcerer)
1 STEAHLTY character...

So for me it's

A fighter, a wizard, a rogue, a cleric, a druid, a ranger


50 % of the party need to cast spells.
75 % of the party need to tank or do ranged attacks

So for me i add a druid and a ranger to that group. The ranger specialised in ranged. The druid, the rogue, the cleric and the fighter tank. One of them(not the fighter...) stay behind to protect the wizard who blast the ennemy with his spells...

[Telonius]

Depends heavily on the style of campaign. But in general, I'd go with Bard first (makes everybody else better at what they already do, and is a party face/assistant skillmonkey), then Artificer (item factory, can create flanking buddies).

[DeathQuaker]

In very general terms, I'd generally choose characters who

1. Rounded out the party with more skills. The core group, if the rogue is your typical dungeoneer who picks locks, disables traps, and sneaks, will be lacking both charismatic skills as well as acrobat-type skills. If the rogue does not have high listen and spot, someone with those skills would definitely be helpful. Since the wizard doesn't get a lot of skill points and needs to boost concentration and spellcraft, additional knowledge skills would also be helpful.

2. Provide combat support either in the form of ranged support or secondary melee (let the fighter tank, but help flank, etc.). Assuming that the cleric and rogue are going to provide melee help, I'd definitely at least make one of your fifth or sixth members an archer and/or ranged spell slinger.

What classes these people take could vary. If we're sticking to core classes and single classes only, I'd pick a Bard--provides buffing, additional arcane spell support, possibly some spell healing so the cleric isn't too much of a healbot, knowledge/lore, and lots of charisma--and a Ranger--useful scouting and survival skills, and can serve extremely well as either party archer or melee support.

Various multiclass builds could also serve similar purposes. You can do some fantastic stuff with fighter-rogue builds in a number of different ways, and a multiclass spellcaster could support either the wizard and cleric so they aren't tapped out of spells while still also either helping with spells or physical combat.

If you're including non-core classes, there's about an infinite variety of combinations you could use.

And of course if we're taking things out of theory and talking about practical play, races chosen can make a difference (if the first four characters have no darkvision, maybe bringing in a dwarf would be a good idea), and moreover, player capability and style-strengths are important factors. If the players are best using certain tactics and abilities together, build for that and not necessarily "class balance". Good players will make just about any combination of classes work (I've been in two games completely sans arcane casters), and bad players will make the classic four-person party unfeasible.... but will hopefully learn from their mistakes.

[Shas aia Toriia]

I'd reccomend adding in something that can help out all your other party members, such as a bard. This person can also double up as the party face if need be.

Secondly, I'd go for some ranged support, in the form of either an archer or a blasting wizard (hey, it doesn't have to be optimized).

Just my two cp.

[Kizara]

I'd reccomend adding in something that can help out all your other party members, such as a bard. This person can also double up as the party face if need be.

Secondly, I'd go for some ranged support, in the form of either an archer or a blasting wizard (hey, it doesn't have to be optimized).

Just my two cp.

Generic Druid, with companion spell and natural spell.

Cleric, with Trickery and Magic domains. (also face)

(what, oh I MUST have 6?! fine....)

Batman

Barbarian leap attack junkey (FB etc) with 1 level in ranger for track.
Remember, you have two people that can cast detect secret doors or knock, 4 summoners and a barbarian right here.

Druid specializing in wild shape (MoMF etc)

Uuummmmmmm..........

...

Artificer or something to make you items? Yea sure, that works.

[valadil]

Personally I like to see groups with variety. I think this is a bit easier to achieve with redundant casters than with redundant melees, especially if the casters are wizards with different specialized and prohibited schools. Our current game has an evoker wizard and a sorc (me) going for incantatrix. We've got enough variety like that, although we should have swapped classes as the wizard has yet to cast a spell that isn't direct damage while I'm dropping Hideous Laughter and Sculpted Grease everywhere. A well played bard can also work as a spare caster, especially with UMD.

For a 6th slot I like weird fighters. It's a great slot for gishes, tactical fighters, and battle clerics.

[MorkaisChosen]

The Archivist from Heroes of Horror would make a good Knowledge-monkey and assistant caster character.

One character that can manage two of the roles that keep coming up (ranged combat and party-buffer) is the (in my eyes) incredibly cool Bard/ Arcane Archer. With a decent number of Bard levels (you can hit Arcane Archer after 8), you can do a good job inspiring the party (inspire courage doesn't need concentration, so you can start it then just keep shooting four or five arrows a turn and keep it going!).

[Devils_Advocate]

There are many ways in which to make a party of 6 characters with distinct roles. The following are just a few examples:

Archetypal, core-only group:
Tank: Gruff, dumb, tempermental Dwarf Barbarian, Fighter, or Barbarian/Fighter
Healer: Human Cleric of Pelor with Healing and Sun domains
Batman: Knowledge-obsessed, detail-oriented Gnome Illusionist with Wis and Str dumped
Skill Monkey: Greedy, morally ambiguous Halfling Rogue, good at breaking and entering
Party Face: Sly Half-elf bard with high Cha and Int, excellent social skills, poor combat skills; contributes to fights mostly with songs
Tracker: Grim, quiet Elf Ranger, good at scouting and archery

(The Order of the Stick has a pretty good mix of classes. Individually they're unoptimized, but as a group, what strengths they have do complement each other pretty well...)

Non-traditional, non-core group:
Tank: Duskblade
Skill Monkey/Tracker: Scout
Healer: Favored Soul
Party Face: Beguiler
Debuffer, Undead Master: Dread Necromancer
Ranged Damage-Dealer: Warmage


Eberron group:
Tank: Warforged Figher or Warblade or Psiforged Psychic Warrior
Skill Monkey/Face: Changeling Rogue
Item-maker/Trapfinder/Blaster: Dwarf Artificer
Healer/Tank: Half-orc Druid
Utility caster/Face/Blaster: Kalashtar Telepath
Tank/Tracker: Shifter Barbarian

Powergamed group:
Artificer
Archivist
Druid
Divine Metamagic Cleric
Wizard
Erudite (I think I heard that they can be pretty uber...)

all with appropriate feats, spells, powers, PrCs, etc.