Keith Harrison on implementing the Hashable protocol in your classes. The implementation of the protocol itself is of course very simple, but the additional information on choosing between hashing functions and avoiding collisions is fascinating.
Refactoring? Radical refactoring? or maybe ... Rewriting?! I really liked this article by Rob Napier who argues that even if you stick by Joel's rule of what you should never do you can still actually refactor an entire project, over time. It'll take you a long time but throughout the process you'll have working, maintainable software. It's obviously only for extreme cases, but I think the approach is solid if you find yourself there.
Talking of refactoring, Jesse Squires gives us some fairly straightforward but still useful advice on how best to get rid of those singletons that are dotted around your app. I really liked his point about using Swift's optional parameters to do "partial" DI as well. Good read.
Custom collection view transitions have been around for an age now, but if you just want a selection of pre-canned transitions between paged cells then you could definitely do worse than this very pretty set from Jin Wang.