Jay is Games is the place to look. This search brings up a list of dozens of choose-your-own-adventure games, complete with reviews, ratings, and walkthroughs. posted by Dojie at 11:15 AM on July 15, 2010
Somewhat closely related -- though it might just be for me because I think of them hand in hand because I used to read the published Zork choose-your-own-adventure books -- you can find lots of fun interactive fiction at the Interactive Fiction Database.
You'll love Project Aon. They're digitizing the old Joe Dever Lone Wolf books so you can play them online. It's like a cross between CYOA and D&D. Give it a go! posted by griphus at 11:44 AM on July 15, 2010 [1 favorite]
This isn't online as such, but's it's free and takes the fabled lands gamebooks and makes 'em into a downloadable game.
posted by josher71 at 10:13 AM on July 15, 2010