I've read so many over the years I doubt I could remember them all. I started all the way back on the Dimensions Online story page. One story that holds a special place was called "Drew and Nicki's Food Fun" if I recall correctly. It was about the characters from the Drew Carey Show. Where he is dating a woman named Nicki who starts off thin and gains quite a lot over the course of the season. This actually happened in the show. As Drew was a big guy and they both enjoyed food together. So, someone wrote a story to expand (no pun intended) on that premise. It was the story I shared with my wife to explain to her feedism and stuff. The actress who played Nicki was the same who played Dr Adison Shepard on Grey's Anatomy. She wore a fat suit as the episodes progressed.
The other that comes to mind are a couple of stories with a common theme. They are about the Munchies. Which are these little Grey blob creatures that cause people to get fat because they are bored. They were from a PSA cartoon from the 80s. Some authors took that and wrote various stories of single people and couples being the victims of the Munchies. Where they are basically force fed until reaching sizable proportions. I think there are some on this site. Otherwise I know deviantart has both stories and even a great comic about them.
I'm sure I could think of others. But, those are particular favorites.