HiTechnic has announced on its website that a new sensor has been developed for the LEGO Mindstorms NXT. It's a compass sensor, capable of providing a digital heading (rounded to nearest 1 degree) to the NXT Intelligent Brick. Very cool. I can think of many uses for this, but the best one would be that the feedback would allow a robot to move in a very straight path and stay on a set course.
Click on the "News and Announcements" section to read about it. Oh, and some (or all) of the User Panel members will get a version of it to test out. If you are selected as a member, contact HiTechnic to find out more details.