Really, “role” is not that important in 3.5. Having a mixed team doesn’t really accomplish that much: the most powerful classes are just simply more powerful. They can handle things they aren’t “specialized” in almost as well, if not better, than weaker classes that supposedly specialize in those things.
So this is basically a run-down of the general class tier list.
These classes can handle anything and everything. With a day’s preparation, they can even handle it easily most of the time. Challenging them becomes a lot about layered defenses and large amounts of misdirection, and even then it is very hard to do.
Team Cleric will crush everything before them, regardless of level. DMM(Persist) can be done from level 1 by being Human with 16 Cha and having the Planning Domain. Or with 10 Cha, and the Undeath Domain alongside Planning.
Team Wizard will too, if the players of the Wizards are sufficiently creative. At very low levels, this will be somewhat difficult, but certainly not impossible. Around level 7, it will become fairly easy. Eventually, Team Wizard is most likely the most powerful team.
Team Druid will probably have it easiest of all, what with the Animal Companion at level 1. By the time they get Natural Spell at 6th, they won’t be stopped except perhaps by one of the above teams. They aren’t more powerful than the Clerics or Wizards, but they’re not really weaker except by the slimmest of margins, and they’re definitely the easiest of the three to make super-powered.
With four of them, these classes should be able to handle anything and everything as well. In some niche cases, Tier 1 does better because it can prepare unusual spells for an unusual challenge. Outside of those cases, though, this looks a lot like Tier 1.
Team Sorcerer isn’t quite as well off as Team Wizard, since even with four of them there are going to be spells they’re missing, but nonetheless they’re going to mop the floor with most everything.
Capable of handling itself quite nicely against a wide variety of opponents, but rarely has that automatic “win button” that Tier 1 or 2 may have.
Team Bard can be devastating if there are a lot of supplements available, particularly Dragon Magic with its Dragonfire Inspiration, Frostburn with Snowflake Wardance, and Magic Item Compendium for the Badge of Valor, the crystal echoblade, and the harmonizing special ability. Eberron Campaign Setting for Song of the Heart, Spell Compendium for a lot of things, including inspirational boost, etc. Book of Exalted Deeds for Words of Creation if we really want to be mean. Talfirian Song from Races of Faerûn also allows a Bardzilla, which is awesome. The Sublime Chord from Complete Arcane could even allow Team Bard to play on close to even footing with the Team Sorcerer, but I’m not sure prestige classes are legit here.
Comes in two flavors, really: can handle a variety of situations, but will struggle with all of them to some extent (Team Rogue), or can dominate a single type of encounter, but is pretty useless outside it (Team Barbarian).
Team Rogue will need to be very careful about using its wands, and everyone will need to max UMD. Still, the fact that they have UMD, plus their general adaptability, means they will be OK so long as they don’t have to get in a huge fight versus undead or constructs or something. Their lives are also greatly improved by a large number of supplements, particularly Champions of Ruin for Craven, Dungeonscape for Penetrating Strike, and Spell Compendium for golemstrike, gravestrike, and vinestrike. Dragon Magic for Dragonfire Strike.
Team Barbarian is beastly in melee combat, but they are going to have a lot of trouble with flying or magical foes, not to mention non-combat problems. Complete Champion’s Lion Spirit Totem ACF will be crucial to keeping them mobile. For most levels, Team Barbarian is very likely to be able to take down anything it can get its axe on very quickly, but things it can’t are going to be huge problems.
Similar to Tier 4, but, well, worse. The specialists (Teams Fighter, Paladin, Ranger) are still pretty useless outside their area of expertise, but now they are not automatically winning the things they do specialize in. The generalists are now having a really hard time handling anything by now (Team Monk).
Team Fighter is in a lot of trouble. Any problem that cannot be solved by smashing its face in, they likely cannot solve. Will involve obscure ACFs and feats for getting various skills in-class, suboptimal ability score layouts, and quite possibly cross-class UMD, which is just ugly. Supplements are critical, since Core alone lacks enough feats to be worth their time. Dungeonscape for the Dungeoncrasher ACF will be important. Fiend Folio’s Feathered Wings graft will be crucial for getting Team Fighter into the air at a level-appropriate time.
Team Paladin and Team Ranger
Where Rangers and Paladins fall depends very heavily on whether Sword of the Arcane Order (Champions of Valor), Mystic Ranger (Dragon vol. 336) and Mystic Fire Knight (Champions of Valor) are available. Battle Blessing (Complete Champion) will also be very important to the Paladin. With these, they are quite capable, at least at early levels, easily keeping up with Team Bard or even better. Without them, they’re pretty close to even with Team Fighter.
Team Monk is just shafted, well, barring Wild Monk (Dragon vol. 324). They’ll all be struggling to do much of anything, and it’s unlikely to work well. Sure, they’ll be hard to lie to, and possibly hard to kill/prevent from retreating, but every fight is going to be an uphill battle. If they have Wild Monk, then they’re going to land somewhere between Team Bard and Team Rogue, most likely; Wild Shape basically solves melee combat for them as well as it’s going to get solved, and it helps some with the MAD situation. Still going to be rough, though.