Depth of Field is a wonderful thing. Many 3D programs can render this, but it takes a deathly long time. After Effects has a plugin called Lens Blur that does a nice job of taking a depth matte and using it to generate depth of field. Most 3D programs allow you to render a depth matte which is basically a black and white image, where white shows things close to the camera and black is far away.
You can even rack focus from the foreground to the background using this plugin. I’m working on a spot for Monster Energy Drink and this is one of the elements that will be incorporated.
The lens blur pugin I’m using is right Here: