Editing curves
I like curves.
One of the guys on the framework team wrote a curve editor that makes it trivially easy to create and tweak the settings for Curve objects.
I highly recommend both this utility and the accompanying doc. A few well chosen curves can do wonders to make your object movement, graphics effects, physics, and AI seem richer and more interesting, and editing curves in a graphical tool is much nicer than messing about with equations or raw control points.
