As far as brand, Canon and Nikon are the two big players, for the most part. Leica is great stuff and their prices reflect that fact. If you're going to be using long focal length lenses for wildlife (almost a necessity) you're going to need a decent tripod. It's just like riflescopes: any movement is magnified. Low light? That means you need "fast" (read expensive) lenses. like any other hobby (think shooting) once you get beyond stuff that's just "good" and "acceptable" it's a real matter of diminishing returns with regard to the price:quality ratio.
