You have several options!
For entry level gaming I would personally go with Lenovo, their newer gaming laptops should have a 2GB video card and I remember some have an option to swap the DVD drive with a second GPU for SLI support.
For medium to heavier gaming, I absolutely recommend ASUS. They have amazing laptops with some of the best reviews. They also last forever and all the newer ones have extremely good cooling. Check NewEgg.com for prices and models they currently offer.
If you want hardcore gaming or a desktop replacement, please, check this site out:
http
/www.xoticpc.com/
15" Laptops you would be looking for start at $900 with a GT 960m with 2GB of VRAM. 8GB of DDR3 RAM and a 1TB HDD
You can customize everything from different processors, to different user upgradeable graphics cards to replacing all the heatsinks with pure copper and the best thermal compounds. You can even have the laptop painted or have a custom graphic embedded in the lid.
Look at a bunch of different configurations and brands, not all of them have the same customizations or interchangeable CPU's, just depends on your budget. You can go up to an 18" laptop with dual GTX 980m's with a total of 16GB of VRAM, 4Ghz+ quad core i7, four extremely fast on board Solid State Drives. The choice is yours.