1. Locate your ancestor and his or her siblings in every census year available, especially for ancestors who were present for the 1880 and later censuses (1880 is the first census to identify the relationship of each individual to the head of household). You might be surprised how often you'll find a parent or sibling living with them. Unmarried sisters, especially, often end up living with family members in later years - and may provide the clue to a female ancestor's maiden name. I recently ran across three elderly sisters living together in the 1880 census -- one unmarried and two widowed -- which provided me with all sorts of new clues once I traced them back through earlier census and other records.
2. Look for naming patterns for possible clues to given names or maiden names used by previous generations. Women, especially in earlier centuries, often passed on their maiden name as a given or middle name to at least one of their children. Men may have also named at least one of their sons after themselves or their fathers. Couples with larger families may have named several of their children after siblings, aunts or uncles.
3. Turn to obituaries for clues to family members, both living and deceased. Even if the parents aren't listed, brothers and sisters can also provide clues to the names of the parents, and also provide a pattern which can help you track down the family in a census record. Some obituaries can be found online, but most are best obtained by contacting the library in the location where your ancestors lived.
4. Estate records, including not only wills, but also probate, guardianship, and other records, are another great source for information on parents. While a bit harder to locate than some record types, estate records have been abstracted and compiled into book form for many communities. These books can sometimes be obtained through interlibrary loan or on microfilm through your local Family History Center. Many great individuals have also volunteered to do free lookups in books which they own.
5. Poring through deed indexes is one of my favorite ways to track down clues to an individual's parents. Grantor and grantee deed indexes are usually organized by surname and can provide a quick glimpse at the people with which your ancestor purchased and sold land. Looking at the land transactions of your ancestor and his/her siblings over a period of time can often provide clues to family members, related families and friends. Certain terms used in indexes such as "et all" (and all) and "etux" (wife) can also help to identify family relationships, while "dower" and "estate" deeds can help to identify possible estate records. Once you've identified a deed which looks like it may provide a clue to your ancestors, request a copy of the original through the local county courthouse or register of deeds.
Hope this helps you add a new generation to your family tree!
