Box UK has a checklist available that should list the most important steps to take when launching a site. It was previously mentioned at Web Resources Depot. While I agree that you need a good checklist, I find the one presented here too oriented towards the layout and the design. Pre-launch marketing is not mentioned, and we know that’s a very important part of a succesfull initial launch.
Still, it can help to build your own strategy, by building on this document. The original can be found at the Box UK site.