You probably have an Instant Messaging app you already use already. Beejive, Meebo, eBuddy, Trillian, IM+, etc, are all pretty serviceable but none of them are as pretty as Verbs. Verbs is the only IM app that looks and feels like it was made for iOS.
What is it?
Verbs, $4, iPhone. It's an IM app. Everybody has one of those. You find a buddy you want to talk to and chat away! What really shines about Verbs is that it doesn't bog you down, the app feels light and is very easy to use. Starting a chat is simple, the little chat bubbles are attractive and managing multiple chats is like the 'tab view' in mobile Safari (zoomed out cards). It displays the current conversations you have open in the top right corner and in its 'tab view' shows you how many new IMs you've missed.
You can also view images, PDFs, Office and iWork docs from the app and it supports CloudApp and Droplr too.
The app is a little limited because it only supports Google Chat and AIM (and MobileMe) and isn't full push like Beejive (Verbs stops pushing after it stops running in the background), so it's not perfect for everyone but it's easily the most well designed IM app there is on the App Store.
Who's it good for?
People who use Google Chat or AIM. People who like pretty apps. People who like to use IM on their phone.
Why's it better than alternatives?
It's prettier and on my phone, that counts for a lot. All the UI elements look like it fits right in with the rest of iOS (and for those who count this stuff, the icon is deeelightful), It's also really easy and familiar to manage the multiple chats you have going on because it juggles them similar to how Safari handles multiple windows open (or webOS card view).
How could it be even better?
But pretty only goes so far! The app is still in its infant stages so it can feel a little bare bones. It doesn't support groups, so all my buddies are thrown together in one super long list. The text input field doesn't expand to fit more text (like the stock SMS app does), so you just get one line that goes on and on and on. Also, push notifications only work when the app is still 'multitasking', as opposed to apps like Beejive where you'll get notifications even if you shut the app down (as long as you're signed in). I don't know anyone who uses anything other than AIM or Google Chat but if you dabble in Yahoo, MSN or Facebook (and a lot of people do), you'll probably have to skip this. Wouldn't mind an iPad version either!
Verbs for iPhone [iTunes]