In order to know what type of RAM to get, you'll need to know what model of motherboard you have, since different frequencies and different sizes are supported by different motherboards.

I personally recommend getting dual channel RAM, because it's cheaper and faster.

As for brands, you can't beat Corsair, but that's extremely expensive as far as RAM goes, so I use Legend, which is nice, as it comes with a lifetime warranty.
Legend is an Australian company, so I think you'll find that it's more than readily available where you are.