I like:
The Clique (series)
The Sisterhood of the Traveling Pants (series)....
In the first novel in the series, it is established that four high school students, Lena Kaligaris, Tibby Rollins, Bridget Vreeland, and Carmen Lowell, are such close friends that they are virtually sisters. They find a pair of thrift store jeans that fit all four girls beautifully, even though the girls are all different sizes and shapes. To keep in touch with each other during their summer vacation, they pass the pants along from one girl to another. First, the pants go with Lena, who is spending the summer in Greece with her grandparents. Lena then sends the pants to Tibby, who is stuck at home. Next, Tibby sends them to Carmen, who has gone to visit her divorced father in South Carolina. Carmen sends them to Bridget, who is at a soccer camp in Baja California, Mexico. Then, the pants go back in reverse order--Bridget to Carmen to Tibby to Lena. When each girl wears the Traveling Pants, she gains insight into her life and is emboldened to change it.
--From Wikipedia =]
The Clique Series is a young adult book series, written by Lisi Harrison. Tweleve novels have been released in the series so far, including the Clique Summer Collection. The series revolves around five girls, Massie Block, Alicia Rivera, Dylan Marvil, Kristen Gregory and Claire Lyons, who collectively make up The Pretty Committee, the A-Lister clique of the fictional Octavian County Day school (OCD).
---They are SOOOOO good =]