Have your own file exchange service
A few months ago I discovered this software gem on StackOverflow (http://stackoverflow.com/questions/2034038/simple-file-upload-download-manager-for-distributing-files):
http://www.thregr.org/~wavexx/software/dl/
It allows to run your own file exchange server and create automatically-expiring downloads (and uploads). It's perfect for emails and quick file exchange. I didn't put an url because yesterday I was moved by reading the following post in the mailing list:
http://thread.gmane.org/gmane.comp.web.dl-ticket-service.general/150
It's rare to see this kind of attitude, and would like to know what HN'ers would suggest to the author to improve this software. The answer on SO mentioning "dl" is also underrated (despite being a much better fit), contributing to the problem.