I've played in so many games it's hard to vote for just one. Most of the time, we either fall short (2 ppl typically) or get about 9-10 party members if Lela is the DM *ducks head for retributive strike by Lela*. In the only D&D game I'm in right now (as the DM as usual), the four players are:
Petro Stonehand, LG Human Fighter (who will later be Cleric/Sacred Fist)
Sujimoto Mariko, NG Human Shugenja (OA Class, uncertain about future multi/prestige classes)
Kira, LG Human Sorcerer (later Dragon Disciple)
Ivellius, (can't find character sheet) High Elven Bard (possibly multiclassing to Fighter and getting Bladesinger or Spellsword)
The bard gets access to Disable Device and Search as class skills, and the Rogue's Traps class ability, so this kinda is the iconic four.
Tank,
Mage,
Healer (Shugenja),
Skill Guy/Trap Finder
In the case of this group, it's good that they are the iconic four, as otherwise they wouldn't have access to the variety of class abilities they'll need to survive.
Isn't it funny, though? The way it seems to work out that way? Mostly because Wizards is so obsessed with the idea that 4 party members are the basic unit, basing XP, treasure, CR, and EL on a party of 4. So the main reason, IMO, is that it is too much work for some DMs to figure out how extra/lacking party members change that. And it's nice to have a well-rounded party, as any serious CRPG player can attest to.