I would recommend Xoticpc.com or malibal.com. Both are Clevo Resellers (xotic sells sager, where malibal is a direct clevo laptop vendor). They have very good pricing compared to some of the other sellers, and have awesome configurations. Plus they have good cooling solutions and support standard MXM style graphics cards which are upgradeable. From what I have read on NBR, Sager has pretty poor customer service, and malibal/xotic have better service, and they have active reps over at NBR. If you PM them they may give you a discount code as well.
I Have been salivating over this puppy: 17" Satori
or you could check out the 15" Lotus the P150HM. Both have multiple GPU options, and I find the pricing similar to xotic in some aspects and cheaper in others.
For $2000 you could get at least a Radeon 6990M, 8gb of ram and an upgraded quad.
Now the big difference is the 17" has 2 HDD bays and an Optical bay. where the 15" has 1 HDD bay but you can buy an Optical drive HDD caddy that replaces the CD drive.
I am looking to get one of these bad boys at some point soon, but have been doing a ton of research and these 2 vendors seem to have it down right, and provide good customer experiences. But I can't say 1st hand.
Hope this Helps