As I've probably said before, usually Yazawa-sensei's manga are shoujo stories, with one or two love stories or couples.
Recently she is trying to write more dramatic and adult stories, like "Kagen no Tsuki".
Here I want to provide a complete list of works of Ai Yazawa from the beginning .. or at least a list of well known works. ^_-

15nen ne [15th year] - A love story with school setting.

RabuuRetaa [Love Letter] - Another schooltime love story, where a student named Hitomi is in love with her math teacher.

Kaze ni Nare! [Become the Wind!] - The story begins when the main character, Yuki, is attending the first year of the middle schools. She decides to join the local Tennis Club where she finds love problems and romance other than tennis match.

EESUKEPU [Escape] - This manga explores a little more the feelings of the character instead of telling about their love problems. It's really more mature than the previus manga.

Ballad made sobani ite [Until the next ballad] - The author is back on character love problems. This tankubon is composed by two different stories: the first being the one which gives the title to the tankubon and the second called "Futari no seaside park".
"Ballad made sobani ite" is set on the idol world. The main character, Hiromi falls in love with a guy who's win the Idol Contest.
The second title "Futari no seaside park" (Seaside park for two) is about a dream date in a special park and the main character is a guy.

Marine Blue no Kaze ni Dakarete [Embrace the Marine Blue Wind] - This is one of the more complex manga by Ai Yazawa before Gokinjo Monogatari. It's composed by 4 tankubon and this means that it's the longest among the ones presented previously.
The story is about romance during the summer and we have the classic love triangle: the female character is in love with one guy while his best friend is in love with her.

Tenshi nanka ja nai [I'm not an angel] - This manga is one of the most popular among the other except for Gokinjo Monogatari. It's made by 8 volumes published as always by Ribon.
The story is about Midori who becames a member of the student council and fall in love with the president of the council.
A funny note: in volume 3 of Gokinjo Monogatari, when the Akindo have their first flea market Midori and Akira make an appereance. Midory buys a bag shaped like a Berry-chan from Mikako.

Gojinko Monogatari [Neighbourhood Story] - The "neighbourhood stories" of a group of students who attend the Yazagaku Gakuin. The main character has a dream: to become a famous stylist, with her own line of dresses called Happy Berry.
Yazawa-sensei most known manga and a true comedy masterpiece.

Kagen no Tsuki [Last quarter of the Moon] - This manga is very different from all the previous; it's the first one which doesn't have a love story as main theme, but it's a story about friendship.
The main characters are a group of children and a girl who is in coma because of a car accident. Plus there is the ghost of a singer in the background.

Nana - The story of two totally different girls with the same name, Nana, who come to live in Tokyo, for different reasons and happen to divide the same flat.
Currently serialized on Cookie Monthly

Paradise Kiss - The official sequel of Gokinjo Monogatari involves some old characters and some new entries.
The main character is Yukari Hayasaka, who accidentally meets some strange guys who attend the Yazagaku Gakuin ...
Currently serialized into Zipper Monthly.