It all depends how in depth you want the lighting to be. I know 118 used their lighting to signal their and other drivers of various things. This year we toyed with using our LED lighting to alert our drive team when we had balls in our elevator. You can use Audrino boards to make some pretty cool custom features. I'm not an expert on that stuff, but if you're really interested I'm sure someone on here can charm in.
As far as the lights themselves go, you have three choices, a
static color and strip,
RGB LEDS, and
Addressable RGB LEDS. This year we stuck with a static white color just to give a little extra aesthetic appeal to our bot. In previous years, we've used RGB LEDS with success.
Purchasing and installing the lights after choosing which lights and features you're shooting for is the easy part. Many cheap LED strips, static, RGB, and Addressable can be found
here.
From there the sky is the limit, here's a picture of GUS' 2012 competition robot.
-D