iOS: Chances are you use your iPhone's camera to take pictures of things you want to remember. Déjà Vu is an app that helps you keep track of everything in your virtual visual memory by taking those photos and using image recognition to automatically categorise them for you. Of course, you can also categorise them yourself, but that's not quite as fun.
You'll need to sign up for a free account for the image recognition to work and to take more than 10 memos, which you'll likely do as creating photo memos is really simple. You don't have to take photos one at a time. Instead, when you enter the camera mode you can just snap a photo, then another one, and so on, until you're done. Each picture you take will show up in a queue up at the top of the screen to let you know it was captured. This has the somewhat unnecessary advantage of being cute, but also reduces the lag between taking each photo and that's very welcome. Since I've had to upgrade to the iOS 5 beta, I'm happy to report it's working fine there too.
This isn't the only way to remember your photos, but it is helpful and free. If you'd prefer to have actual notifications with your photos, check out PhotoMind.
Kooaba Déjà Vu (Free) [iTunes App Store]