for LEGO® Robotics
HiTechnic manufactures a variety of products that integrate with the NXT:
Acceleration / Tilt Sensor
EOPD (Electro Optical Proximity Detector)
HiTechnic has released a new IR sensor: the IRSeekerV2. It has enhanced features to detect modulated and un-modulated IR signals.
Update 9/22/09: The new IRSeekerV2 is now supported in ROBOLAB. Download parts 1 and 2 of the update from here.