WordBreaker is a fun game Facebook has a really well-designed app Leaflets offers a nice iPhone-formatted version of the New York Times and del.icio.us ThinCloud and PocketTweets are two great Twitter clients Movies.app can be useful for finding show times
Oh yeah, and don’t forget about Fluther!
I just mentioned it on another thread here, but http://launchrz.com is a great way to find good webapps. All the above apps can be found there. I also like FlickIM, Jivetalk, and SeekPod.
Just check any social site that you use for example; Stickam the webcam community will be making a program, facebook already has a program, REAL will be making a program, and myspace is in the process of making better prorgrams.