Exact date of marriage for individuals who married. Location of marriage for each couple, both the civil jurisdiction and the denomination and name of the church, if the marriage occurred in a church. Keep in mind that many individuals remarry after the death of or divorce from a spouse. Date of death for each individual, including infant and child deaths. The cause of death is useful but death certificates are much better than family information for this item.
Cremations are extremely rare before the current generation.
For individuals not born in the U.S., the date of immigration. The date of naturalization is less useful. It can be tremendously rewarding to trace family likenesses through several generations. One common place to get information about U.S.-resident families is from federal census records. The federal census has been taken every ten years since 1790 and shows who was living in a particular household in the given census year.