Tweetie 2! Really doubted I'd pay for a Twitter app, but this one is worth it. Really full featured, but also very simple.

How do you compare it to Twitterfon? Does it allow multiple accounts?

Yep, sure does. and so many nice things are integrated - like being able to email someone a tweet. The UI is great, too -- little things like scrolling off the top of the list refreshes the feed.

I really like tweetie 2. Every developer should own it just to see how the refresh works. It's so intuitive! I find myself trying to refresh Facebook that way.

I'm so late, but I second this! I was really reluctant to pay for a Twitter app, but it's totally worth the $2-3. It's the little things, like the reply all feature. It's so nice not having to copy and paste usernames into a reply!

Okay, okay - I love Twitterfon, but you guys are convincing me to try Tweetie 2.

Really awesome list from Mashable: 70+ Free iPhone Apps for Social Media Mavens.

Another cool-sounding social app:

Twitter 360 Offers Augmented Reality Tweeting for iPhone 3GS

http://www.intomobile.com/2009/12/01/twitter-360-offers-augmented-reality-tweeting-for-iphone-3gs.html#ixzz0YhcXJaQH

Tweetie 2 has some great features, but I'm currently an Echofon Pro (formerly TwitterFon) devotee.

You can now check in at malls and stores and share with the community on FastMall, also video and photo reviews of anything you want :)

I have to say, Yelp's got a check in feature now, too, that's pretty interesting. Of course, facebook is the grand daddy of them all.