Other Halves, And Other Tales is a remarkably good Kingdom Hearts work. It's now an AU fic because it (and its sequel, Paint The Sky With Stars) were written before Chain of Memories and Kingdom Hearts II, and it describes the lives of most of the Square Enix characters in Traverse Town after the first game is over. There are several original characters by the end, but they avoid being the Spotlight-Stealing Squad too much and share the limelight nicely with the original characters. A lot of it has to do with the romantic pairings (Sora/Kairi, Riku/OC, Aerith/Cloud, Leon/Yuffie, and later a brief Cid/OC), but it shares space with plenty of humor. You can find it here.