The Clevo x7200 based Sager NP 7280
is single handedly the most configurable and powerful laptop available, as of right now I would wait until a sandy bridge version is released.
I would only go with a Sager for a few reasons.
1. Their cooling is unsurpassed.
2. More customization options than any other brand.
3. Excluding the MOBO almost every part is user upgradeable and easily accessed.
-My Sager unit has 3 back panels one giving me access to my HDD and one for my RAM (this is typical), but the third gives me direct access to my GPU and CPU for easy upgrading in the future.
This unit can be configured with a desktop i7 and SLI GTX 485m (each with their own heatsink and fan, the most powerfull laptop GPU which are approx equivalent to the desktop variation of the GTX 460. With a SLI 485m configuration this laptop can easily skyrocket past $4000.
If you are looking to build your own unit expect to pay more than you would configuring one on a site like http://www.xoticpc.com/
as you are buying parts in small quantities directly from a supplier.
Things to look for;
-Bare bones clevo / sager units (includes only mobo, chassy, possibly screen)
-Laptop GPU suppliers (keep in mind the GPU you purchase must be compatible with the mobo MXM slot)
-W/ the X7200 you will be able to use a desktop i7, rather than finding a mobile proc supplier.
-HDD and ram will be easily found on newegg and other such sites.
-A wireless card again will probably need a supplier but you may be able to salvage one from an "older" device.