Vernier Sensor Adapter for NXT
Vernier Sensors will make their adapter for the NXT avaiable in October. You can find this adapter from LEGO Education.
With this adapter, any of Vernier's 40+ analog (BTA) sensors can be incorporated with the NXT. Vernier sensors can be purchased at http://www.vernier.com/.
Update: Use the following link to view more details of the adapter: http://www.legoeducation.com/store/detail.aspx?CategoryID=159&by=9&ID=1442&c=1&t=0&l=0 (If the above link causes trouble, the item number of adapter is W991377 on the www.legoeducation.com United States site.)