I'm going to avoid more recent artists/albums, since it's really not fair to call them "essential" already. There are a few exceptional albums that could fall under that category, but otherwise it's just too soon.
Also, if I add a Belle & Sebastian album it'll probably be one of their first two (Tigermilk or If You're Feeling Sinister). As I said, I want to avoid more recent stuff, and those two are the most defining albums B&S have put out. Guided By Voices will definitely be on that list though.
Also, You Forgot It In Me is more widely accepted as BSS's best work. It may prove to be one of those exceptional exceptions.