The Examples.zip file on this page contains the sample code accompanying the book, "Learning OpenGL ES for iOS".
There are several interesting stand alone samples including a bumper car simulation, particle effects, COLLADA model loading, and a partial reimplementation of Apple's GLKit framework. You need a copy of the book to maximize the utility of these samples, but you are welcome to download, examine, and reuse these samples even if you don't purchase the book. I appreciate feedback in the errata section of this site (link on the right side of this page).
NOTE: All examples were updated October 31, 2012 to change project settings and eliminate warnings introduced in Xcode versions 4.2 through 4.5.1.