One of the general recommendations I've seen on this forum is to base your choice on the lens system rather then the camera body, and then to put your money into the best glass you can afford. While this makes sense I'm a little confused. Because of the way things are marketed its quite easy to compare bodies, glass however seems to be more difficult to get a good reading on (at least from a newbe perspective). Also how does third party glass such as Sigma/Tokina/Tameron fit into the equation. Can some of these lenses be cost effective alternates to OEM glass without sacrificing quality. How does one search out the gems among all of the available glass?