I recently conducted a very thorough research in this very area when I wanted to build my new gaming laptop. Many brands are ...eh ok, and all should come with discrete graphics (SLI on the higher $ end) but you'll want to look for incorporation of recent technology into your build, i.e. USB-3.0, RAID capability, eSTAT, etc. I specifically focused on the systems using the new Sandy Bridge i7 CPU.
Clevo (Sager uses their barebone systems) has a few nice ones for customization (here
). These come standard w/ eSATA, 2x USB 3.0, & allows choice of 1080 or lower resolution screens.
What I eventually went with was the MSI MS-16F2-ID1 (Specs Here
) because it has 2 internal HD compartments on a 16" system allowing RAID, something only the larger 17.5" Clevo systems came with. I filled these with 2x 256GB Crucial C-300 (SATA III) SSD hard drives (RAID-0) resulting in a super-fast & highly power efficient array. My system boots to desktop in under 20 sec & easily lasts over 3 hours due to the low power consumption of these SSD drives. While laptops have yet to incorporate SATA III technology, that I've heard, using 6gb/sec drives ensures your system isn't bottle-necked at the hard drive. Other features of this MSI model are up to 16GB DDR3 1333 RAM (which I maxed out), 1080 resolution, HM67 chipset (used the i7-2720QM Sandy Bridge CPU), 2x USB 3.0, 2x USB 2.0, eSATA, HDMI out, GigLan, hi-def audio, & integrated Blue-tooth/wireless-N.
Note: I stopped looking after finishing my build, about June 1st, so there may be another model out now to give my MSI a run, but for system prowess, configuration, and incorporation of the newest technology, it was hard to beat a couple of months ago.