We wrote about Dropbox in our 10 free social apps for the Mac feature recently (it's also available for Windows and Linux), and we're fans of the service for its easy and convenient cross-platform cloud storage and sharing capabilities.
Now you can tap into your Dropbox account from your iPhone as well. It's not intended as a standalone app, so if you don't already have one the software will prompt you to create a free 2GB Dropbox account. After that you'll be able to view files, listen to music, or even watch videos stored in your Dropbox folder right from your phone.
If you already use Dropbox on the desktop you'll know about and appreciate its automatic sync features, but surely because of potential space limitations the iPhone app thankfully doesn't actively sync your entire Dropbox collection. But it does support automatic downloads to your phone, and "favoriting" a Dropbox file will set it up to auto-sync. When a new version of the file is available on Dropbox, you'll be notified in the iPhone app and prompted to sync.
Other features of the app include easy one-click sharing of your Dropbox files by email (a link to the file will be sent to the recipient), and a photo gallery view for easy browsing of images in your Dropbox account on your phone. You can also upload photos and video directly to your Dropbox, which when combined with Shared folders can quickly and easily share your media with friends and family.