Another unique Sigma telephoto, the 120-300 f/2.8 (along with the 100-300 f/4) provides a range and aperture not available from anyone else. A very sharp lens that focuses quickly with hypersonic motor drive. A favorite of sports shooters, especially on the sidelines for football and basketball.
Note: at almost 6 pounds this is a heavy lens. Unless you are really strong you will want to shoot from a monopod.