First thing you do is sign up for 'Find My iPhone,' now free from Apple:
http://www.apple.com/iphone/features/find-my-iphone.htmlI do have a MobileMe account and the best thing about it is how well it syncs my personal stuff. Apple is finishing a massive data center in NC and I hope it means a major expansion in features.
I have downloaded hundreds of apps, mostly free ones that I only used once. I will just list the apps I use often to now and then.
My data apps are, SimpleNote, Evernote, Dropbox, 1Password, Omnifocus and MindNode.
The first three are free. Simplenote is my quick note program. It syncs instantly with the web based version. I often am recording thoughts and switch back and forth between my iPhone and the web. I find the evernote interface clunky, but it does have its uses. 1Password is a Must, at least for me. There is an iPhone app and a desktop app, Mac and PC. You can sync via Dropbox, but that makes me nervous to have my database of passwords, credit card info etc, so I sync at home via WiFi. Omnifocus is expensive, especially if you have the desktop app to compliment it, but it is a great place to work on lists, projects, and processes. I use it for anything from business projects to grocery lists. MindNode is a great, simple mindmapping tool that also has a desktop version.
I just bought an app called 'Due' (dueapp.com) that it a great reminder app. Fast to record reusable tasks and timer with great 'snooze' functionality.
I have Navigon installed for GPS, but keep in mind it takes up 1.6GB.
Camera+, Instagram, QuadCamera and Hipstamatic are fun camera apps. Instagram is more of a social media app.
Speaking of social media, I don't do Facebook, but the app is supposed to be pretty good. I do do Twitter and the official Twitter app is great. There is a free app called 'Boxcar' for people who want notifications from multiple social apps. It is highly recommended by many.
Video apps: Netflix and Hulu Plus of course. You can get MSNBC live on Justin.tv with their app.
Radio apps: I am addicted to radio apps on my iPhone. Pandora and AOL Radio are great and free, but WunderRadio is the best radio app imo. You can get to almost Every radio stream online on your iPhone. I've rigged a direct feed into my car radio and stream all over town and on major highways between cities.
The catch for you is not being able to do data and voice simultaneously, which would be a deal killer for me. We've got another year in our contract with AT&T, which is just as well. If this changes down the road, I will definitely take a look at Verizon.