What 8gb memory upgrade would you recommend for a Lenovo IdeaCentre H500s Slim Desktop?

It has 4gb of memory. What brand and and type of memory would you recommend?

RAM: DDR3 SDRAM
Memory Speed: 1600 MHz

Hi
if your windows operating system is 32 bit then you are wasting your money as you can't use more than 4GB

Any reputable brand like corsair, and you will need DDR3 SDRAM, and as the speed of one of your RAM sticks is 1600, its not worth getting anything faster or slower than that (as it will default to 1600mhz for dual channel) unless you will be changing that out.