Right after going over how to key in class, I stumbled across this in depth tutorial about how to finesse the color cast that can sometimes be a problem when shooting on green screen. This is a very in-depth tutorial, covered in two parts, that goes over different methods of removing green screen spill in After Effects. Unfortunately, I'm having a hard time embedding the videos, because they are unlisted, but you can watch both of them here.
I particularly like how this tutorial covers so many different techniques to achieve the same result, as well as advice about when to use them. Furthermore, the most advanced technique (limiting the green channel based on the average of the red and blue values) is explained clearly and with a lot of attention to the mechanics behind it.
The red-blue average method also has a plugin that you can download to achieve the same result on a single layer, which is very convenient. This plugin also looks useful for further green screen effects, because it allows you to create an alpha channel based on just the spill light. There are a lot of possibilites that this opens up, including using it to create a light wrap effect to further integrate green screen footage into a composition.
