I'm a journalist. I take notes. Sadly, my handwriting is awful. I can barely read what I write the day after I write it. I type faster than I handwrite, too. So Evernote is my note-taking app of choice. It runs on all four platforms I use (a Windows desktop, a Macbook, my iPhone, and my iPad), synchronizes content among them all, indexes everything, and has neat bonus features like a voice recorder and camera integration. No matter which of my devices I'm using, it gives me access to all my notes and stories, since I also compose most of my work in Evernote. It's a tech journo's dream tool. And if all you want to store is text, the free version is plenty robust enough. I pay for the premium version of the app because I like it, not because I need to.
One thing Evernote is not so good at: Keeping lists of things to do. Things is an especially elegant to-do list manager that works across Apple platforms: iPhone, iPad, and Mac OS X. It has great features for organizing items by date, project, or tag. Like Evernote, it syncs your data across its supported platforms.
The downside to Things is its expense: Each platform requires a separate paid app. But for list-keepers, it's worth a serious look.
It's just a little grocery list for the iPhone, but of all the apps that do this task, I find ZipList the easiest and by far the fastest to use. It automatically categorizes your purchases--you'll see "milk" and "cheese" in the "dairy" section--which makes shopping more efficient. You don't have to learn a thing to use this app. Just enter in the stuff you need, and then check it off as you walk down your store's aisles filling your cart.
Speaking of grocery shopping, Epicurious' iPhone app features a great database of recipes, with user reviews for all. I use it at the grocery store when I want a recipe that goes with ingredients I know I have, or that I'm looking at on sale at the store. I check out the recipes using those ingredients, pick one I want, and it tells me what else I need to buy. The recipes are pretty tasty, too.
This is the iPhone's view into the SugarSync data synchronization service. I use this product to keep my PCs and Macs all up to date with each other, and for data backup as well. The iPhone version lets me see, basically, all my files, everywhere. I mostly use it to access my growing photo library, but from time to time it's handy to have access to old documents and the like. You can also share files with friends from within SugarSync.
It seems that most tech nerds prefer competitive service Dropbox, but SugarSync gives you more flexibility when it comes to tracking and syncing files on your desktop and laptop computers.
Please note: If you're going to use a sync service like this on your mobile phone, it's imperative that you set up password security on the device. Otherwise, anyone who picks up your phone could get access to all the files on your PC or Mac.
The iPhone Facebook app is uniquely suited to the smartphone. It gives you a grid of popular options, a secondary page where you can store shortcuts to the profiles of people you keep in touch with, and it gets appropriate push notifications--when anyone comments on a wall post of yours or sends you a message, for example. It's one of the best phone versions of a major Web service I've seen.
Like Facebook's own iPhone app, Twitter's own app is a very strong player, competing solidly with also-excellent third-party apps like Tweetdeck. Twitter for the iPhone is fast (important on a slow network connection) and has the standard important features like photo service and geotag integration. I was a loyal Tweetdeck user until this app came out. It's just a little faster to use, and that makes all the difference.
Routesy gets real-time bus and train location data from the Nextbus service and puts it in a handy iPhone app. I use it to tell me how late I'm going to be for work. Its nice little features include geolocation, so it knows what bus stop you're closest too, and a bookmark list of your favorite routes and stops.
There are few things more frustrating than talking to taxi dispatchers, at least in my hometown of San Francisco. With Taxi Magic, you can kiss that awkward, sketchy conversation goodbye. The app geolocates you and can send you a taxicab at the press of a button. It will even tell you where your booked taxi is and when it's due to arrive at your location. You can also use it to pay your fare.
Only one taxi company in San Francisco is on the Taxi Magic system, but that's enough. It's a great, useful little app.
TripIt replaces the file folder of confirmations and directions you used to take on trips with you. The Web services takes all the itinerary info you get e-mailed to you as you're planning a trip, and automatically categorizes and sorts it for you. People you're traveling with can also update your itinerary, if you let them. The app gives you a one-stop place to find it all, sorted by day.
I still carry a folder of printouts when I travel, as backup. But in a year of business and vacation trips, I haven't needed it.