I rely on for synchronizing files between machines and maintaining a backup of important files. The  app allows me to access my files on the iPad, but until recently it was difficult to get a file into Dropbox from an iPad app that doesn't explicitly support Dropbox.
Taking advantage of the Dropbox API, Habilis has created a simple service that lets you email files to a personalized address and have them appear in your Dropbox. (Dropbox competitor also recently instituted this feature, but I prefer Dropbox and it's used by most of my colleagues for sharing files.)
To test the service, do the following:
Within a few minutes (depending on your network connection and the size of the file), the file appears in a new folder called From Habilis within your Dropbox folder.
(Thanks to and  for alerting me to this great service.)