Sample letters for complaints and petitions can be found on the U.S. Government's website. There are specific forms for specific types of petitions as well as a general form for filing a complaint. There are also several non government websites that have sample forms.
There are dozens of sample forms on the Internet. Many are available to download in PDF, Word or some other popular format. As expected, the U.S. Government's website contains several petition forms that are related to government and law. There is also a general complaint form for consumers who need to take action against a person or company if they have received bad service or products. In addition, there is a complaint wizard that takes the consumer through several steps to draft a letter based on the nature of the complaint.
Go Petition contains several pre-filled forms for several popular and current causes. Topics deal with global and International problems like saving endangered animals in Indonesia or calling for better care in nursing homes in the United Kingdom. Go Petition also offers the opportunity for an individual, group or a business to start their own petition for free by signing up for an account.
The U.S. Government and Go Petition are just two examples of where a person can go to find templates for complaints and/or petitions. A simple search on the Internet for "sample complaint forms" or "sample petition forms" will lead to many more options.