Honestly all of her book are essentially the same - young people cope with loss, etc. etc. - but the best imo is Goodbye Tsugumi. She does a good job of creating the scenery that really brings that novel alive.
Amrita. Although I've read all I can get my hands on that Banana has published, and to be honest, I haven't found anything quite like Kitchen. Amrita is my fav next to Kitchen, but if you find another good one, please share. :D
Someone suggested me "Jinsei no tabi wo yuku" as my next book, but I feel it lacks what made me seek more of her.