Dexter Industries (who makes all kids of cool NXT sensors) has just submitted a few lesson plans / ideas to http://www.k12lab.com (an part of National Instruments who created NXT-G in conjunction with LEGO)
So far they've submitted lessons for:
Thermal Infrared Sensor (TIR) -Measuring Heat from a Laptop exhaust fan -
and their Solar Panel - Constructing a Solar Car
They've included sample programs for LabView for LEGO Mindstorms (LVLM), but even if you're not using that language, you could adapt to NXT-G or any other one.