Loopt uses location technology that lets you see where your friends currently are. Perfect app for keeping track of that significant other, and a must have for any stocker.
I haven't used AIM for a while, but now that it's available on the iPhone, I'll be using it a lot more. Chat me up on AIM, screen name = TheBobBlog
When you hear a song and wonder what it is, just hold you iPhone to the music and within seconds Shazam will tell you the artist and track name. It's powerful too, I've been able to capture background music playing in stores.
Clowdy is location based so you can see what photos people have taken around you, Just take a photo, click "Post", and it's published.
There are many movie apps out there, but I found this one works the best.
Control your iTunes anywhere within your Wi-Fi network right from your iPhone.