[madhouse]

Flowers for Algernon by Daniel Keyes.

Read it first when I was 16, at the recommendation of my literature teacher in high school. For the past... - darn, this was long ago! - ...more than 20 years, I've read it at least once a year, and intend to do that for as long as I can read.

That book changed me, like nothing else since.

[btschaegg]

Happy to see this mentioned here. While I can't claim that it was "lifechanging" for me, I still maintain it to be one of the best SciFi novels I've ever read.