How to make NXT bricks communicate information? Is it possible to connect, in some way, two NXT bricks that has program functions running on both. For example, Brick one would tell brick two that it is okay to start a program. Are there any sensors that could facilitate this type of communication?
You can use the Bluetooth mailbox feature to pass messages back and forth between 2 NXTs.

If you want to use sensors, you could use the HiTechnic NXT IRLink Sensor (NIL1046) and NXT IRReceiver Sensor (NIR1032).