Back in late October 2010, I wrote an eBook about the Sprint Retrospective for the Seapine Agile Expedition. This "how to" eBook discusses the basics of the Sprint Retrospective, but is not specific to Scrum. The practices can be applied to any Agile or Iterative and Incremental process. For more information, read "Look Back in Agile: The Sprint Retrospective" .
There is also a supplementary blog post on The Seapine View that talks about how to identify and select the highest priority actions that result from the retrospective. After inspection, understanding where the team should focus their energy on adaptation is key to any Agile process. Read "The Restrospective: Priortizing What Matters" to find out more.