Fighting Fantasy series of books. After much "umm"ing and "ahh"ing over which book to choose, I decided against the first in the series - Warlock of Firetop Mountain - and went with Deathtrap Dungeon instead.
The Fighting Fantasy books were a series of "choose you own adventure" type books with some added dice-rolling to resolve combat against monsters. They first appeared in the early 1980s and were interactive books and games all in one. They were some of the first proper 'novels' (if you consider these books as such) I read after The Hobbit and the first half of Lord of the Rings (it wasn't until I was in my late 20s that I read the whole lot). They were also my introduction to roleplaying games. I fondly remember collecting a whole stack of them - together with my best friend I think we had all of the first 20 or so and I read most of these (often more than once). I think I also had the Sorcery! books, one or two of the Lone Wolf books as well as a few other similar books that were published at around the same time.
Now, I have to admit that I did used to cheat whilst playing/reading these books. I'd keep my finger on the previous page in case the new page I turned to resulted in the death of my character. That way I could "rewind time" and choose the less-deadly path. I think I also cheated sometimes with some of the dice rolls.
These new Fighting Fantasy apps are great. They reproduce the whole thing on the iPod, together with the occasional pieces of (coloured) artwork that were in the original books. Rolling of the two dice is done for you with a shake of the device which produces some accompanying 3-D animation, and you can access your character sheet (and each stamina-reviving food) whenever you want. As with many ebooks, the text can be resized and changed to a variety of different fonts. The app also automatically bookmarks where you last were. It feels just like reading the real thing.
Unfortunately though, it doesn't let you cheat. If you take a wrong turn or make a bad choice and your character dies, you have to restart from the beginning. Which, of course, means rereading all the pages you've been through before (unless you choose an alternate route) after rerolling up another character.
Deathtrap Dungeon was probably the third FF book I bought when I was a young teenager and, I believe, one of the hardest/deadliest of the series at the time. Certainly, in this electronic iteration, I found my character dying quite a few times. This was not helped by being specifically told that you character will need several items in the dungeon to get through. Therefore there is a tendency to try every door and pick up every object you come across. After my character had died half a dozen times, I started to get somewhat cheesed off having to skip through all the numbered paragraphs to get to the same point again to try a different course of action (damned stupid Buddha-like idol).
Otherwise, it's great fun and very well put together. Although I'm suspect it's only of interest to those over 30 who remember the original books. Still, if you want to try something similar online, the Project Aon website hosts most of the Lone Wolf gamebooks, which are free to play.