If its a case you want have a look at this one from Savastore click here
If you want one with everything else inside it (mobo, cpu, hdd, ram, etc) click here
Memory - what do you do on your PC? What do you expect from it? If you want your PC to be really fast, then get around 1Gb of ram. For normal computer use around 512Mb is enough. What memory you buy depends on the motherboard.