I'm a big fan of the web-based software RequestTracker, affectionately known as RT.

It is similar to Bugzilla, except it's not software bug oriented so much as "Stuff To Do" oriented. It has a simple email gateway, it keeps track of absolutely everything, it allows you to add custom fields quite easily, it changes priorities of your events over time, and it allows you to keep track of how much time you've spent on various projects. Around my office, it's pretty key.