First things first. There is no such thing as a real gaming laptop – not if you mean a laptop machine that is portable, battery powered, and has game performance comparable to a desktop machine with a good graphic card GPU in it.
Why? Because a good graphic GPU requires a lot of power, it’s bulky, and generates a boatload of heat. Look at a modern GeForce or Radeon card – they are thicker and heavier than many notebooks all by themselves. The heat generated by a graphic GPU is a major problem for laptops, and a high end GPU draws up to 150W in power all by itself, which will drain a typical laptop battery flat in 20 minutes or less.
There are a few very large “Desktop Replacement” notebooks with 17″ or 19″ screens which run on AC power only and include desktop class graphics cards, but these don’t meet the criteria for a laptop – namely being portable and battery powered.
What can you get?
Entry level – abandon gaming ambitions: For low cost laptops, you are going to get integrated video which is built into the motherboard chipset and uses ‘shared’ graphic memory (which really means it steals memory from the main system RAM of the machine, which is the slowest and least efficient way to do graphics). These models will either not run games, or will run games at the lowest resolutions and quality settings only. If you are thinking of a laptop under $500, then basically forget about modern games, and use a desktop or a game console for your game playing.
Mid level – gaming possible with limitations: Midrange laptops can come with discrete video chipsets which have their own, faster dedicated graphic memory. These GPU chipsets are almost always still soldered onto the motherboard, they can provide a good boost in video performance, to the extent that they will play modern 3D games at lower resolution, and less demanding games resonably well. The AMD A-8 series processors which have a Radeon HD 6550D graphic core is an example of a cost effective midrange laptop. The Intel HD 4000 graphics with an i5 or an i7 processor is just slightly lower in performance than the A-8 / HD6550.
‘Gaming’ laptops – middle-range gaming performance at a higher price: Higher end ‘gaming’ laptops use Mobile versions of high performance GPUs which have been designed for lower voltage, lower wattage and lower heat output. It is a balancing act between performance, heat and battery life. There are a number of different chipsets to choose from — be careful about the exact model numbers, for example the GeForce GTX ###M series cards are excellent performers while the GT ###M series are much lower. You can get medium settings on many games with good frame rates, and some games you can get full resolution and high settings depending on the chip. The trade off is a larger computer, a high price, and lower battery life. Some units have two video GPUs internally, one gaming GPU and a lower powered integrated GPU for normal work, so you can turn off the gaming GPU while you are on battery power.
If you are deciding on a new laptop, and doing some entry- to mid- level gaming is important, then research the GPU chipsets that are available, and check the performance of your favorite games with the GPUs.
A benchmark chart of gaming performance for notebook computers is here
Frame rate tests of specific games on notebooks
Here is an April 2012 PCMagazine article on their top ten gaming notebooks from $1000 to over $4000 and a PCWorld article on five gaming notebooks from August 2012