I think storyboards are probably the most significant change to iOS development since the SDK was released. Matthijs Hollemans has a long but comprehensive tutorial taking a look at the whole process of storyboarding in iOS 5.
... and don't forget part 2!
Carl Brown with a small, focused category to make NSRegularExpression a little easier to use. Part 1 of this article is also worth checking out if you are new to regular expressions or need a recap.
Jeff LaMarche with some small, simple samples of using GLKit on iOS 5. Is GLKit OpenGL ES for the rest of us? It certainly seems to be heading that way.
Here is some more GLKit goodness, you lucky lucky people.