Alphabet iPhone Cases: Created through Jessica Hische's Daily Drop Cap project, these cases are each decorated with a different letter from the alphabet. The cases would be perfect for typeface enthusiasts. I also just really like having my belongings stamped with my initials.
Electronic Bookplates: I came across this really awesome DIY project on Design Sponge. Leaving a book at a restaurant or on a plane can be one of the most annoying things ever. Now that so many of us use tablets as our books, among many other features, it's a bigger deal than losing a paperback. Borrowing the nameplate concept from paperbacks, Max teaches you how to create a nameplate for your devices' screens so that if they do happen to be left somewhere, your name is the first thing everyone sees. It's also just a cool customization idea.
Mac App Icon Sets: Our desktop icons are something we stare at on a daily basis and click on multiple times a day. Why not customize them if you can? A lot of sites out there have icons sets you can buy. I don't personalize all my icons, but like a little variety when it comes to my chat apps.
Android Icon Packs: Similar to Mac icons, you can also customize your Android phone. The first step is to get a Launcher, which will enable you to change your icons and customize your settings. Once your Launcher is set up, you can download Icon packs and choose a set that you like to customize the way icons look on your phone.
Personalized Cases: Another easy way to personalize is to do it with sleeves and cases. Etsy always has a wide variety of customized cases. Two of my favorite ones come from LoveyDoveyCreations for iPad sleeves and rabbitsmile for both iPhone and iPad cases.