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.
Spot the Signs. Do you have a good relationship with your manager? Is he or she relatively reasonable? Do you have regular one_on_ones where you talk about your career goals and growth? If so, it's likely that your boss will accept your resignation with grace, help develop a plan of action for your last two weeks, and maybe even attend your farewell happy hour.