There are a few good candidates for this one, since the list includes Most Everything I Had To Read In School, with some major exceptions where I also hated them. Here, though, is the most notable and surprising example:
Jane Eyre, by Charlotte Brontë
There was a trick to this one: I didn't read it in class. Because of the year I spent living in Estonia, I was not able to take the placement exams before entering high school, and didn't manage to get into the AP class until midway through the year. By that time, the class was already deep into Jane Eyre, and hating it vocally and abundantly. It seemed impractical for me to join when they were so far into it, so my teacher had me read Lord of the Flies instead, which everyone else had already done. This was a win on TWO levels, because I really loved Lord of the Flies, whereas my love may had been tempered by classwork... and, it gave me the opportunity about nine years later to finally give Jane Eyre a try.
As you may recall, I have a not-so-good relationship with Jane Austen, who is sort of on a similar playing field with Ms. Brontë, and so I didn't exactly have high hopes for this one. Ironically, the main reason I decided to finally read it was because I thought the most recent movie adaptation looked cool (AND THEN IT KIND OF WASN'T). But! to my immense surprise, I did like it. I didn't love it, but I found it engaging and enjoyable enough. The reason was twofold: first, I liked the creepy gothic horror of the whole setup, and second, I found Jane to be a stronger and more relatable character than any of Austen's brood, and while I continue to find Mr. Rochester pretty deplorable and continue to puzzle over the scores of literary women who find him somehow deeply attractive (seriously, I don't...??? did you miss the part where he is creepy and aggressive), I think Jane holds up well enough for it to be a good read.