Big displays are great for many purposes especially for displaying time, temperature or even scrolling text/graphics messages. In following project LED dot matrix display does this job along PIC18F252. As you may know such number of LEDs cannot be controlled directly, so there are LED driver chips used (STP16CP05) that allow controlling LEDs dynamically row by row.
Temperature is measured with help of well known LM35 temperature sensor. Device also has an automatic brightness control where ambient light is measured with light-to-voltage converter (TSL257) and then LED brightness is adjusted according to readings. To make things more interesting and flexible there is also an IR remote control implemented. So settings can be changed remotely in case you stick display higher on the wall.