This 4GB SDHC card comes preinstalled with Raspbian Wheezy, a Linux Debian based operating system optimized to run on the Raspberry Pi.
It's nice and convenient to have it pre-loaded instead of having to download the image. Ultimately I ended up going to a 32GB card, but this was a nice starting point.
MCM is our low cost, high product value source. Same quality as the more expensive vendors, without the "expensive." Always fast and dependable.