If you're interested in making your own temperature-control system for a soldering iron, then the following project by Dangerous Prototypes forum member carlazar will be of interest. Their system is relatively simple, and uses an Arduino to monitor the signal from the themocouple in the iron. Then the temperature can be controlled with a simple LCD/button menu system. You only need a few parts apart from the iron, Arduino and LCD - and the entire system can be powered from an inexpensive notebook computer power supply.
Looking for a rapid-use LCD for your Arduino projects like the soldering iron controller above? Save time and move forward with the Freetronics LCD & Keypad shield which contains a bright 16x2 character LCD and five buttons that can be read from only one analog input pin: