The Alienware X51 from Dell now has an Ubuntu Linux option for gaming on Linux. Highlighted from the product page is using Steam for gaming on Linux.
The Ubuntu Linux X51 system pricing starts out at $599 USD and goes up to $1049+ for a higher-end model. The low-end model is powered by an Intel Core i3 3220 with a NVIDIA GeForce GTX 645 while the higher-end model is with an Intel Core i7 3770 and GeForce GTX 660. Yep, Alienware is using NVIDIA GeForce graphics backed by NVIDIA's binary blob for powering their Linux gaming rigs.
Those interested in more details on these Alienware systems with Ubuntu Linux can visit alienware.com/ubuntu.