In terms of iPhone apps I'd recommend checking out Headspace, Duolingo, Detour, Simple, Drafts, Fantastical, and Scanbot. All of which I use on a daily or semi-daily basis.
Detour is best used in San Francisco but they are expanding soon to more cities. It is an app which takes you on GPS based guided walking tours...but it's so much more. It's more like stepping into a documentary where the documentary is physically around you. They include sound effects, interviews, music, and information about the area. Each detour is centers around a theme or area of the city you're in. It's done very, very well. I can't recommend it enough. Very affordable in comparison to the more touristy, traditional walking tours. And as this is GPS based, the app knows where you are so you can go at your own pace. ANNNND you can sync up multiple iPhones into a group detour. It was the best thing I did in San Francisco and I'm dying to go back to go on more detours.