In The Royal Tenebaums (2001), fashion plays a important role in characterization. The characters are defined by particular looks that play a subtle comic element in the film. Costumes were designed by Karen Patch.
The looks of the children influence their later looks, especially Margot and Richie. Margot is featured in stripes a child and an adult while Richie maintains his athletic look with headband until his character is transformed.
Margot's sophistication as a child transfers to the signature fur coat look below left. An earth tone camel color dominates Margot's looks and several characters in the film. 
Above both of Margot's lovers are in the same earth tone camel, which re-appears below on the father as well. Chas, played by Ben Stiller below right, keeps a distance from the rest of the family indicated by the bright red track suits also worn by his sons.
In Ghost World below from 2000, the characters were based on pre-existing cartoons. The costume designer had to bring to life two-dimensional figures of the imagination. Mary Zophres was the costume designer for this noir comic book aesthetic.
Sophie Carbonale created the look for Legally Blonde (2001) taking inspiration from Goldie Hawn in Shampoo and Los Angeles sorority girls and their love of pink.
Betsy Heimann constructed all of the clothing for Almost Famous (2001). She based Kate Hudson's jacket on a look in The Apartment (1960) in combination with groupie style from her own experience at the Continental Hyatt House in the 60's.
The 2000's see similar films emerging at similar times. Above Chicago (2001) costumes by Colleen Atwood shares the cabaret aesthetic with Moulin Rouge (2001) by Catherine Martin & Angus Strathie. Below, the Harry Potter films begin in 2001, featuring long robes and bearded wizards, costumes by Judianna Makovsky. Also in 2001, the Lord of Rings appears with long robes and bearded wizards, costumes by Nglia Dickson & Richard Taylor.
Above, Troy from 2004 shows the Spartan soldier look. The costumes by Bob Ringwood emphasize the raised brush on the helmet, breast plates, fabric skirt bottoms and the long spears specific only to Sparta.
Above left is the original Greek soldier look which would have been a naked or loosely wrapped man with a small helmet, short knife and large shield. The Spartan, described above, introduced the breastplate, helmet with brush for cleaning shoes and the long spear. Finally right, the most recognized aesthetic of the Roman gladiator. His look used the short knife of the Greek but took the breastplate and helmet with brush from the Spartan and considerably reduced the size of the shield. Below Gladiator from 2000 with costumes from Janty Yates. Crowe plays gladiator general Maximus who comes up against the heir to the throne Commodus. During the Roman empire, royal figures were obligated to fight gladiators once a year to prove their strength, however the royals often had the gladiator's arms broken before the battle to ensure royal success.
Below the Ocean's Eleven phenomenon that emerged in 2001 was based on the Rat Pack film of the same name from 1960 featuring Frank Sinatra, Dean Martin, Sammy Davis, Jr., Peter Lawford, Joey Bishop and Rob Davis. The films emphasize suits for all characters in order to allow the clothing to be a background to the diversity and personalities of the celebrities.
Resemblance characterization became extremely popular in the 2000's, Above Ray (2004) by Sharen Davis emphasizes the importance of the suit and led to Ray Charles sunglasses being released. Below Walk the Line from 2005 had costumes all personally created by Arianne Phillips.
Above the resemblance characterization of Frida from 2002, costumes by Julie Weiss. Below Aviator from 2004, costumes by Sandy Powell. The representation of Katherine Hepburn included the iconic masculine look but also showed the more feminine side of the actress.
Below Brokeback Mountain from 2005 was the result of costume designer Marit Allen's investigation into cowboy subculture. Levi's are for horse ranchers. Wranglers are for cow ranchers. This subtle distinction is loaded in the subculture. Below the characters are similar but the key transformation is Jack's character who starts with a black Texas style hat and then ends the film with a light colored hat the resembles Ennis' Wyoming hat.
Indie cinema and its eclectic quirky style resulted in challenges for the fashion designers. Above the complex narrative and character development of Eternal Sunshine of the Spotless Mind (2004) led the costume designer Melissa Toth to change the hair color of Kate Winslet from blue to orange, as well as costumes. Below Little Miss Sunshine from 2006 had a rainbow color palette created by Nancy Steiner that emphasized the bright primaries throughout.
Well know for her strong use of thoughtful color palettes, Milena Canonera created the costumes for The Life Aquatic with Steve Zissou in 2004. She combined the ocean blues with the bright orange of a life jacket and white, seen on crested waves and clouds.
More indie films with quirky thrift store characterization continued in Napoleon Dynamite from 2004 by Jerusha Hess and Borat from 2006 by John Alper.
Quentin Tarantino led the way in the 90's for establishing post-modern indie character looks but he turned to well established costume designer Anna Sheppard for Inglourious Basterds in 2009. Sheppard was responsible for previous war epics Schindler's List and The Pianist and created all of the costumes her self with a Berlin Taylor. The unique hat below left was inspired by Elsa Schiaparelli right.