Pretty much as everyone else has said, you might as well grab a Momentus XT unless you are willing to go the optical bay route.
As for memory, grab any quality, branded 8GB kit that meets the specifications. I personally went Crucial as they were available at a very good price from OcUK (the price has gone up since but it may be that the RRP or wholesale prices have risen), but just look around for the cheapest shop that sells compatible memory. There is nothing in particular that is better than the rest. Some will say 1600MHz memory is a good move, however, there is usually a premium there that isn't worth it unless you are gaming on the system.