In rebuilding one of our Definitions of Done, I came across this excellent resource from the Scrum Alliance: Definition of Done: A Reference.
One of the best points that the article makes is that the DoD is a very unique and specific document for every team (and every project). The article gives the example of the "Done" Thinking Grid, outlining many of the possible areas to check for doneness:
If you're working on a DoD, or just want to review yours, I highly recommend reading the whole article. Lots of great ideas and points to check. Scrum Alliance, Definition of Done: A Reference