The Purloined Pony, classic CYOA, now on Fimfic! · 1:15am Apr 6th, 2014
If you never read this grand Choose Your Own Adventure story back in the day, I'd really suggest giving it a try:
Admittedly I haven't re-read it since 2012, so I have no idea how well it stands up to time... I do recall having LOTS of fun with it, though, and not putting it down until I had explored EVERY branch. I liked it enough to reference it in Shutdown, so it definitely made an impression on me!
(And if you know of any other really good CYOAs please leave me a comment letting me know!)