I have a personal project I'm working on which requires an automatic download link. You know the sort of thing - like you get on SourceForge: "Your file will download in x seconds". And then the file download dialog pops up.
The basic part of the trick isn't limited to Drupal at all, you just HTML:
<meta http-equiv="Refresh" content="1; URL=http://www.yoursite.com/system/files/downloadfile.ext" />
So here, after one second, the page refreshes - except it's a file to be downloaded, so your browser does the right thing and gives you a download dialog box instead.