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.
I ordered batteries and a set of test leads. I received them within three days of when I ordered them and I got a great price. Fast service and a great price - what more could you want.