Range of tier optimization would definitely be a good idea for a new thread, or an adjunct and addendum to this one.
Fighters have fairly high customizability, and so can range anywhere from tier 3 to tier 6, whereas any of the ToB classes remain fairly stable at tier 3, but very certain and specific combos (just 2 or 3, and mostly due to rules (mis?)interpretations) can become very powerful and very broken, but in general, they're solid tier 3 and there's not much you can do to move them away from that (it's VERY difficult, if not impossible, to make even a tier 4 warblade or crusader; given the usefulness and power-stability of the maneuvers they get by default, you simply can't do it).
Wizards (and by extension, sorcerers) have the highest variability of any class in the entire game, moving from tier -1 (well beyond merely broken) to tier 7 (even worse than a mildly-optimized commoner), depending on spell selection and play, whereas druids pretty much can't be screwed up unless you just don't use their class abilities at all, and remain tier 1 or REALLY high tier 2 unless you TRY to muck them up.
Maybe we should rank them on an individual basis?
Wizard: Tiers -1 to 7
Druid: Tiers 1 to high 2
Cleric: Tiers 1 to 3
Commoner: Tiers 6 to 4 (See: Infested with Chickens)
...Etc.
Of course, access to prestige classes should have some bearing on it as well. Wizards have tons of PrCs which add to its range, where classes like dread necromancers and artificers pretty much have to stay in their base class because they have so few options.