D&D 3.5 Class Tiers

Tier 0: Nothing (no published class is this powerful, but some builds can be with options like the Incantatrix or near-infinite power point abuse.  Other prestige classes like Illithid Savant, Beholder Mage, or Shadowcraft Mage can get you here.)

Tier 0.5:  Erudite (Spell to Power variant), Psionic Artificer

Tier 1: Archivist, Artificer, Cleric, Druid, Shaman (Kalamar), Wizard

Tier 1.5: Cleric (Evangelist, Spontaneous), Death Master, Druid (Spontaneous), Erudite, Shaman, Sha'ir, Spirit Shaman, Psion, Tantrist, Templar (Athas), Urban Druid (not the ACF), Wu Jen

Tier 2: Binder (w/ Zceryll vestige), Favored Soul, Sorcerer, Truenamer (w/ Conjunctive Gate)

Tier 2.5: Ardent, Beguiler, Dread Necromancer, Factotum (w/ Font of Inspiration), Imagist, Mystic, Shugenja, Wilder

Tier 3: Bard, Binder, Crusader, Psychic Warrior, Ranger (Mystic), Spellthief (Trickster), Swordsage, Warblade, Warmage

Tier 3.5: Dragonfire Adept, Duskblade, Factotum, Healer, Incarnate, Jester, Nightstalker, Psychic Rogue, Ranger (Wild Shape), Shadowcaster, Totemist, Warlock

Tier 4: Adept, Barbarian, Fighter (Dungeon Crasher), Kundala, Paladin, Ranger, Rogue, Scout, Spellthief

Tier 4.5: Brigand, Divine Mind (w/ Mind's Eye updates), Dragon Shaman, Fighter, Hexblade, Lurk, Marshal, Monk, Ninja, Savant, Sohei, Soulknife, Truenamer

Tier 5: Bard (Athas), Battle Dancer, Courtier, Gladiator (Kalamar), Inkyo, Knight, Noble, Master, Magewright, Mariner, Mountebank, Samurai (OA, CW w/ Imperious Command), Soulborn, Swashbuckler

Tier 5.5: Divine Mind, Samurai (CW), Expert, Gladiator (Athas)

Tier 6: Aristocrat, Commoner, Warrior

Others: Eidolon, Eidoloncer, Mlar, Truenamer (no optimization), the various racial paragons (these classes can be taken at 1st level, but they don't function as base classes in the usual way, so they don't get a tier rating).