You'll have plenty of time to vent personally about your work grievances as you leave, but really, you stand to gain nothing by putting negativity into your resignation letter. And unless you're leaving the state and your current industry, you always run the risk of running into the same people later on. So you're far better off taking the high road and making sure your exit is a classy one.
Your End Game. When you hand in your resignation, it can kick off a bit of chaos__your position will need to be filled, but your duties will also need to be covered until they can replace you. As part of your resignation letter, it's a good idea to convey what your availability is during that transitional period.