Before the 1790 enumeration, there were some colonial censuses taken. Some of these are actually tax lists or quit rent lists. Others are lists of people taken from oaths of allegiance, such as by the colonial government of Maryland in 1776. This particular enumeration has been compiled by Bettie Stirling Carothers and is available in the Family History Library in Salt Lake City. Some extractions of colonial enumerations can be found online. Pre-1790 colonial lists for Connecticut and New Jersey are at Pre-1790 Colonial Census Records.
Before 1790 and in between decennial enumerations, you may find your ancestors on miscellaneous type censuses such as sheriff lists or town lists. They were taken to keep track of the comings and goings of the people in the town or area and what crops they were growing. Some also were created to keep an eye on suitable militia recruitments. To look for these, check the Family History Library catalog at FamilySearch International.
Many state enumerations were taken between decennial years. They help to fill the gap for missing children who have died, left home or remarried. Not all states took these enumerations, but many did and are worth checking. A good place to start is to check state by state at the Family History Library catalog. Some of the best state enumerations are for Iowa. With limited availability in earlier years, they are for 1836 to 1925. The federal government funded some state enumerations, such as for Nebraska in 1885. This in-between census helps close a gap between 1880 and 1890.
School census records are extremely helpful. These were taken through the years to keep track of the children of school age. Some are listed in family units or with the parents' names included. If they show the children's age, they are even more helpful. You may be able to locate them in courthouses or archives. Don't forget to check local or area historical societies, museums and school administration offices.
Colonial era church enumerations can be helpful in locating families. Where the church was established and supported by the government, you may find extant records. This is particularly true to New England states and also Virginia. Once again, browse through the Family History Library catalog to see what has been published or microfilmed.
As more and more records are being digitized, it is important to check the FamilySearch.org's pilot program at http://labs.familysearch.org (click on Record Search). Always check the state archive or state library web sites for the states that you are researching. Look under databases, resources and digital images.
Your research is not complete unless you add some of these census enumerations to your to-do list. They may take more time than you expect, but are worth the effort.