My iPhone has totally become part of my life, and I love always having it with me and the feeling of staying connected. There are so many fantastic apps available in the iTunes Store, and I enjoy trying out new ones every now and then, but I take a decluttering stance when it comes to keeping them on my phone. If I don't use an app for a few days, I get rid of it (I like only having three pages of apps!). But there are a few apps that I use all the time - several times a day, in fact! (I'm only linking to websites, not the iPhone apps themselves, but you can easily find them if you want.)
Tweetie: I enjoy using Twitter, and it's even more fun to tweet from my iPhone. At first I used the Twitter mobile site, then switched to Twittelator, and now I'm hooked on Tweetie, since it has a clean interface that does just what I want.
Facebook: I actually use Twitter to update Facebook, but the official Facebook app is so convenient for checking up on my friends. It does a great job of letting me know what's going on, and the photo browsing (with tags) is fantastic.
Mint: Since I love being super-organized, I'm a big fan of the Mint website, which has all my financial information at a glance. The Mint app for iPhone is really clean and simple, and I have fun making sure all my money is in the right place, or how much I've spent on toys or fast food this month!
Pageonce: This service is another account aggregator (a little like Mint when it comes to finances), but also includes utilities and other bills. The iPhone app doesn't have the coolest interface, but it lets me see my info easily. The best features of Pageonce are the cell phone monitor (which shows me my minutes and estimates if I will use them up or not), and the daily finances update that quickly shows me what my retirement accounts have made (or lost) for the previous day!
Amazon: Since I buy almost everything from Amazon, I'm always using this app to browse prices and check order status. I also love being in a store and seeing something cool, then adding it to my wish list right there so I won't forget about it!