Dave W. mentioned that Mindsensors.com is possibly working on speech synthesis for the NXT... a quick trip over to the website also shows some new items such as a motor multiplexor, allowing you to add up to 4 more motors - it plugs into one of your sensor ports. You can pre-order and it ships after July 20.
Also seen is an RCX sensor adapter, allowing you to connect the legacy sensors to the NXT without using a converter cable.
There's also a RCX-to-NXT Communication adapter - it doesn't say much other than it's used to "enable 2-way communications between the RCX and NXT."
And the other items mentioned as 'in the works':
Binary Tilt sensor
Pneumatic Pressure Sensor
Check it out here. Click on the "Coming Soon for NXT" link to see it all...