You will need:
LEDs, (see above for colour) available from here
Resistors, available from here
A building (kit form is easier to install lights in)
A power source (probably the auxiliary output of your main controller)
Step 1: Wiring.
Step 2: Installation.
Step 3: Street Lights.
Step 4: Tips, Tricks and Ideas.
Power: my layout uses the 12v DC power supply from my controller and all the resistors are 1k ohm versions. The same setup will run from a 16v AC power supply, but the lights are quite flickery with AC. For buildings with more than one light and for different voltage levels, I recommend using this to determine the resistor values: http://led.linear1.org/led.wiz. My lights are powered from terminal strip which is in turn powered by the controller (see pictures). This saves on wire and also allowed me to include a switch to turn the lights on and off when I want to.
I think that's all I can say, so thanks for reading and please feel free to leave any comments and questions.