I've mentioned Photo Flashback on MacStories before – a simple utility for iPhone and iPad, this app lets you easily find photos taken on the same day in the past. Unlike web services like Carousel or Timehop, Photo Flashback is entirely local to your device, as it looks for photos that match the current date in your photo library.
Photo Flashback works well with iCloud Photo Library (I have nine years of photos in it) and today's version 1.4 makes it even better. Soon, you'll be able to check flashbacks on your Apple Watch (clever idea, considering the presence of a Photos app for the device) and the Today widget now takes you directly to a photo in the app. If a photo you tap in the widget is stored in iCloud, Photo Flashback will download it for you.
I know that Timehop supports photos from the local photo library as well, but I've never needed all the other social features of Timehop, and I like how Photo Flashback works for me.
Rediscovering memories through old photos can be hard, and I'm glad that something like Photo Flashback exists for iOS. The app is $0.99 on the App Store.