If you go to the Gigabyte site and look up your motherboard there may be a list of memory that has been tested with this board. Not all brands will be included in such a list, but it gives a starting point.
I normally just stick to major brands with memory...Corsair, Kingston, Crucial, Mushkin, etc. They generally have a lifetime guarantee on desktop memory. I've had very good luck with G.Skill also.
Places to shop...Amazon, Directron, Newegg, Mwave...I'm sure there are many others if you are in the US. Newegg is just the easiest to navigate for me.