Lightest 15 inch gaming laptop

Dell XPS 15z 2.51kg
Options for Core i7-2640M, 8GB RAM, 1920x1080 LCD & Geforce GT 525M graphics card.

Dell Latitude E6420 14" 2.07kg
Options for Core i7 2720QM, 8GB RAM, 1600x900 LCD & NVIDIA NVS 4200M (GT 520M equivalent)

Best gaming results:
Lenovo IdeaPad Y470 14" 2.2kg
Options for Core i7-2720QM, 8GB RAM, 1366x768 LCD & GeForce 550M graphics card.

+1 On the lenovo Y470. Sweet laptop there, but if I'm not mistaken, the 15"(y570) version with the 555m doesn't weigh much more.

Edit - I lied. The Y570 seems to be about 2.7kg. The DV6-6135dx is about 2.51kg, and even though the Y470 is a 14" laptop, I don't think you'll be dissapointed. I'm almost upset I went for a 15.6" (dv6-6135dx) just cause it seems kinda big.

Thanks for the quick replies guys. Much appreciated.
One thing I forgot to mention is that the graphics card must not be the bottleneck. It's gotta either be a card designed specifically for running programs like Catia V6 and similar, or something like an NVidia card like the 560Mx with 2GB of DDR5 RAM. Quad core would be a big advantage, also. I know that I may be asking a lot but I'd like the laptop to last me as long as possible.
Cheers.
Satmel.

Try HP DV6 6170se.

I own one. Its awesome with the dedicated 6770m 2GB DDR5.  

http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en...

That pretty much rules out the 2.5 kg limit.
Anything else you left out? Like a budget limit? This is going to get expensive.

Do us a favor answer the rest of the usual questions we want to know about.
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The Y470 is gonna be the best gpu/weight/cpu combination.

If you get a 560m, it's in a new class of laptops, good luck finding one under 3-3.5kg.

Thanks for your help fellas.  

I've decided to go with the HP8560W with the following (since work is paying for it!):
Windows 7 PRO64,
Intel Core i7-2720QM Processor,
15.6 FHD WVA f/CAM Display,
16GB 1333DDR3 4DM Memory,
750GB 7200RPM Hard Drive,
2Gid NVIDIA Quadro 2000M Graphics Card - Unfortunately, only comes with DDR 3,
Backlit Keyboard,
BD/DVDRW UB Optical Drive,
and the usual stuff bundled with it.

I believe the weight will be 3Kg, which, considering what it will be packing, is not bad.  
There is just one problem - I have to carry it between work and home  

I'll have time to put it through it's paces over the Christmas break. Let you know how it went.

Thanks again.