Never be unavailable to chat quickly with friends again using AOL's AIM iPhone app. Yes, the app uses your AIM screenname to allow you to stay online when you're not at a computer, but it also pulls in your Facebook and Google chat friends, allowing you to easily interact with pretty much everyone you know. (That is, should you want to chat with everyone you know.) Another perk: It lets you send free text messages.
Filling up your new iPhone? Just hoping to make the one you already have even better? These are the apps you don't want to be without.