Drop.io is a simple and private file sharing site that is under-appreciated, IMHO.
For no charge, one can upload a 100 MB worth of files and then share them via a URL (which you can specify). But that is just the tip of the iceberg, your new site can be password protected, others can add to and collaborate on the drop (e.g. – each drop is given a phone number which can be used for conference calls; in addition, people can leave voicemails via another number), and it will automatically expire in a period of time that you determine.
Usage #1: You need to send hi-res photos to Susan which are too big to email. Use drop.io.
Usage #2: You are in a class which relies heavily on commentary work–of which there are only 1 or 2 copies each in the library. A classmate graciously agrees to scan the applicable commentaries and post them on drop.io. Voila! A file sharing website makes everybody happy.