HiTechnic has done it again with the introduction of their newest sensor: The NXT IRSeeker. The new sensor does exactly what it is named for: it seeks out infrared light sources. Outfitted with an array of infrared sensors, the IRSeeker has a 135 degree field of vision. With the multiple sensors inside, the IRSeeker can display approximately where and how far away an IR light source is from the sensor.
One real world application that HiTechnic has pointed out is locating the infrared RoboCup soccer ball.
HiTechnic has take it one step further by detailing the process of programming the new sensor and how to use it in your NXT programs.
You can check out the IRSeeker and more information at HiTechnic.