Nice work with your book, I really like the cookbook idea. It's very useful for beginning and more experienced programmers.

I have a habit of bookmarking useful code snippets, so let's kick start this section

Besides the code snippet page on the wiki I've also come across this ones. I guess a few things are already in your book, but I'm not going to bother with cross referencing.

forum title (comments) - link
100% working solution for the pinch-zoom & pan-move with boundaries control?? - http://www.cocos2d-iphone.org/forum/topic/19178
HKTMXTiledMap (more efficient tile map implementation) - http://www.cocos2d-iphone.org/forum/topic/17945
Additive Coloring Solution? Thoughts? (tinting sprites with a certain color) - http://www.cocos2d-iphone.org/forum/topic/20487
[code] Water ripples (top down ripples) - http://www.cocos2d-iphone.org/forum/topic/25090
Pixel Perfect Collision Detection using Color Blending (performance can still be improved) - http://www.cocos2d-iphone.org/forum/topic/18522
[Class] Flocking/Steering Behavior/Boid class - http://www.cocos2d-iphone.org/forum/topic/9710
Adding UIGestureRecognizer support in cocos2d - http://www.cocos2d-iphone.org/forum/topic/8929
Random Tile Maps - Computer Generated TMX - http://www.cocos2d-iphone.org/forum/topic/6343
Breaking Glass: ShatteredSprite - http://www.cocos2d-iphone.org/forum/topic/19523
Help with Electricity (add additive blending to make it cooler) - http://www.cocos2d-iphone.org/forum/topic/370
Notifications in OpenGL (Like Openfeint) - http://www.cocos2d-iphone.org/forum/topic/5269
Device Camera Overlay and Real-time Manipulation - http://www.cocos2d-iphone.org/forum/topic/14918
Saved state encryption (encrypt saved data with AES256)- http://www.cocos2d-iphone.org/forum/topic/6982
How To Give Your Game Dynamic Background Music - http://www.cocos2d-iphone.org/forum/topic/9247

I didn't see the board message that this section is only intended for fully working code snippets. In that case this topic would be more appropriate in the suggestions section. Not all links have fully working examples.

Great post. I think its fine to keep it here for reference even though its not a single fully working piece of code. They seem sufficiently interesting and I'd like to take a look at them.