Sigma 70-200mm F2.8 EX DG Macro HSM II
Overall, if you appreciate the limitations of this lens and stick within its practical limits, it provides much of the performance of the camera manufacturers' equivalents at a much lower price. If you're looking for a budget fast telezoom for low light or action work, then this is the lens for you.
Casual sports and wildlife work or general-purpose short telephoto portraiture and landscapes.
Macro / close-focus work and handheld telephoto shooting, where the lack of image stabilization puts you at risk of camera shake in images take at slow shutter speeds.