What Nikkor lens is affordable yet great for sports and outdoor photography?

80-200, 80-400

What does "affordable" mean? No lens worth having is under $400 and there are many that go much higher because of the quality of the glass used. Grinding lens glass is an expensive deal and no company can afford to give that quality away.

Here's an excellent place to do research. I would only remind you that buy cheap, get cheap.
http://www.bhphotovideo.com/...video.com/

A used 80-200 f2.8 AF-s is an interesting budget alternative for nikon's own 70-200 as is sigma's 70-200.

Depends a bit on the sport. I've had some success with a simple 70-300VR and outdoor kids' soccer because it doesn't move as fast and I could get close to the action.

I personally use the 80-200mm which is a great lens… Make sure you get the af-s version though unless you don't mind manual focus. The Af-d version is fantastic (I use it) but is a slow autofocuser so I use it manually…