I've owned just about every major brand...from my experience, Sager (Clevo) is the best. I've owned 2 of them and they were rock solid. Best part, is they can be fully customized so you can upgrade anything which is a huge plus. The newer alienware series can now be upgraded but you will pay way more for the name. ASUS make pretty rock solid "gaming" laptops, and have hands down the best ventilation/air flow, and battery life.
Ask yourself exactly what you want as well....do you want just a gaming laptop, or a portable desktop replacement?
Sager 9377 series: 4th gen i7, 800-900m series cards with SLI options, can customize ram, hard drives, msata, network, sound etc. Also has the option of a 120hz screen. These laptops can play BF4 on ultra at around 50fps. This would be overkill if you are just looking for source games...but if you want a machine you can play pretty much any new gen game at respectable frame rates this is your option. Keep in mind these laptops weight ALOT and need proper air flow. Used you can snag these for your price range or slightly under. Brand new they start around $1800.
Alienware 18 R1 - Not quite as customizable as the Sager, but still a machine with all high end specs. Slightly bigger and heavier than a Sager. You will not find these under $2000...no 120hz option.
Good Gaming Laptop:
ASUS g75 series: 2nd-3rd gen i7, 670m card, 8 gig ram, 500gb 7200rpm hard drive...cannot upgrade anything except ram. This is a good solution if you simply want to play source games or non demanding RTS like starcraft, dota, LoL...etc. There is also a specific model that has a 120hz screen. Used they are down to around $1000, new you will still pay around $2000 (don't ask me why, no clue)
Sager 9170: Same stats as the asus, however better video cards. You can get one with either a 580m or 675MX, which both blow the 670m out of the water performance wise. You will only find these used now, roughly around $1000. Also has 120hz options for screen
Alienware's M17x R3 would be the equivalent, or possibly better than the ASUS. This specifice series are known for having many random "issues". Once again you will pay more for the name as well. You will also be dealing with Dell customer service with any issues....so keep that in mind. You can still get these from time to time off Dell's outlet site for around $1800 new. Used they range in price from 1000-1500 depending on the video card. Most of these models have the 460m or 560m which is significantly weaker than any mentioned above...however some do have the 580m. 120hz option available via upgrade cost.