Nikon 80-200 F2.8 lens. The football match between Kuwait & Brazil was a good chance for me to try out it's low-light capabilities.
I had previously tried photographing night-time football matches with the cheaper 70-300 lens, and had never found any photos acceptable. The lens was so slow (F5.6 at the tele end), that it made focusing virtually impossible, and the resulting images were soft and blurry.
The new lens is a stellar performer. Even without AF-S, the focusing is very fast. I mounted it on a monopod and set the ISO to 1000. The images (though a bit noisy) are tack sharp and very usable.
This lens (for approx $800) is currently the best value for money from Nikon (apart from the 50mm F1.8 - which, at $90, is the deal of the century).