I agree that the sexiest and sleekest look is for your components to be hidden away in a nearby closet. However, that introduces complexities like longer cables (perhaps very long depending upon the distance) which can be especially daunting if the plasma has all A/V connectionas on the display as opposed to an accompanying A/V box, having to run IR repeaters, not being able to see front panel displays for devices that don't have outputs to a display device, etc. So, this may not be a great option for everyone.
If you have quite a few components currently and think you may add more, you could go with an enclosed rack to sit under your plasma. The plasma would still be mounted and it's connections run through the walls, but the connections would run into the back of the enclosed rack, so they are never seen. It's a different look than having the components sit exposed on a rack. Personally, I think it's a much cleaner look.
Some companies make enclosed racks that are wider than they are tall. This look makes them more visually pleasing than a narrow, vertical rack underneath your plasma. You could also go with a vertical rack offset from the plasma, like maybe in a corner so that the plasma is hung all by itself in a given section of wall.
I have wide enclosed rack setup underneath my plasma using a Salamander Synergy Triple 30. The unit is a one-piece design that has 3 side-by-side sections ~30" high. It's good looking and certainly fits its purpose. Here's a link:
My wife and I have even put pictures on top of the unit so that it looks less like an equipment component and more like regulare furniture. They also offer a Triple 20, a Twin 20, Twin 30 and Twin 40.
Hope this gives you an alternative to consider.