moTweets really got me to "get" Twitter which I am convinced is better served mobile. Most of the features that you would find in a desktop Twitter application, but in an easy to use, attractive mobile app.
This application protects the data on my phone: call logs, texts, media files, etc. to an online locker that can transfer that data to a new phone. You can also archive. For example, you can keep old texts in My Phone's online locker and have them deleted from your phone. Another interesting feature is that this program will upload location data when it syncs, so if your phone is lost/stolen, you could get its whereabouts.
This app will "listen" to music and check it against an online database to tell you what song is playing. It will also try to listen to you hum/sing, but this method is less accurate...or maybe that's just my singing.
It's YouTube...on my phone. Quicker and easier than going to the website, but it's lacking a few features. I'd like it to be easier to get the link to share via Twitter and Facebook. There is an icon to send via email.