Welcome to the Drupal community, prospective Summer of Code students! :)
This is a list of projects that Drupal community members have proposed and have generally been agreed on as desirable and/or important projects. If you are new to the Drupal community, or if one of these ideas looks appealing to you, these can be a great starting points for writing a Summer of Code application!
However, you are also encouraged to submit you own proposals that have absolutely nothing to do with the ideas outlined here. What's your pie-in-the-sky dream for how great Drupal can be? Found an area of Drupal that could use some work, and have just the plan to see it fixed? Have an idea for a project that could open Drupal to new target markets and use cases? If so, propose them to http://groups.drupal.org/soc-2008 and get a feel for what the community thinks!