Also, the socket type of your processor will determine the motherboard you get. So do you know if the AMD you want is socket AM2 / AM2+ / AM3 at all? Is it Anthlon or Phenom, those would be the ones to get for gaming.
GIGABYTE makes good motherboards, a few others I know are ASUS and MSI. Just give us more info and you shall receive more in depth help.
For RAM I know that G.SKILL is good (which I am using currently), CORSAIR is also recommended, OCZ I hear is fine. You should also get 2-4GB for a gaming system.
For video cards there is ATI and nVidia. Both are very good. Brands that make good cards XFX, Sapphire, HIS, EVGA, ASUS, VisionTek, PNY. I don't know much about nVidia but I know that any card in the ATI 4000 series would be good for you like the 4770 or 4850.
Now, are you building this whole thing from scratch? Which leaves a case, a hard drive, a dvd drive, a power supply.
For a case I would suggest Cooler Master
Western Digital makes good hard drives
LiteOn, Sony, Samsung make dvd drives
CORSAIR makes excellent power supplies.
Do you already have a monitor? and a keyboard and mouse?