AnandTech has written a review of some of the highest-end notebooks that are available on the market, you can check out their roundup over here.
As usual, if you're not in the market for a heavy, high-performance notebook it's unlikely you will be interested in any of these offerings. Battery life is horrible, typically lasting around one hour for moderate usage scenarios. As such, the mobility aspect should be viewed more as a UPS/battery backup instead of something that you will be able to use to go mobile. (Note that we'll look at the Alienware M17x separately in the near future, as it has slightly different mobility aspects.) These notebooks do have the ability to function as desktop replacements for many people, but again performance is going to be lower than what you can get in a similar cost desktop. The benefit is that you can easily pack up a notebook and carry it with you, and there are people that do exactly that, using these as mobile workstations. Now let's take a closer look at these three notebooks and see where they excel and where they may fall flat.