I will have an 8 hour layover in Beijing and would like to see the Great Wall.

Oh, your time is enough to visit the wall and the Badaling section is recommended. You can hire a taxi for a round trip, or directly book a half-day tour through a travel agency. Then I believe you will fully enjoy your day. If interested, I recommend TravelChinaGuide to you. Their contact number is traveltravelchinaguide.com!