These days, third-party lenses are all the rage. Sigma and Tamron released their fantastic 150-600mm f/5-6.3 super telephoto lenses. Both of which are reasonably priced, deliver outstanding performance, and garnering fantastic reviews.
However, not everyone has a grand laying around for the Sigma Contemporary, Tamron , or the orgasmic Sports version from Sigma that will set you back about $1,800. That's a fantastic price considering what you get, but it's still a lot more than most people have to spend if they are hobbyist, amateurs, or just getting started out. This is where my sleuthing skills paid off once again.
I present you the Sigma 100-300mm F/4 HSM EX IF. Built like a talk, sharper than I could have possibly imagined for a fairly old lens (5-8 years), and about 3lbs. I found an insane deal on eBay for this one and there are a few more priced under $600 left out there from reputable sellers. This is a rare lens. So rare that Sigma doesn't even list it on their website. I found that strange as they list all kinds of old lenses.
The more I dig up, the more I think they may have over-engineered this one. Sample photos on flickr and pBase show incredible wildlife images. Videos on youtube from a few years ago show brilliant sharpness and beautiful bokeh.
I recently shot a baseball game between College of Sequoias and Fresno City, using my Canon 60D and an Opteka monopod. The Autofocus was super fast, and manual focus engaged amazingly well. I love using this thing. Check out the sample gallery below.