The Society Security Death Index (SSDI) is a great resource for documenting death (and often birth) information for ancestors who died within the last 20 or 30 years. Several websites have SSDI databases, including rootsweb.com and familysearch.org.
Access to the SSDI is free. If you find your ancestor listed in the SSDI, you can contact the Social Security Administration to obtain a copy of his/her Social Security application, which would provide details including date and place of birth, and parents’ names.
Instead of relying on someone’s recollections, make sure your records are accurate by taking the time to verify the information you have on ancestors who have died more recently! You can read more about the SSDI by going to wiki.familysearch.org and searching for SSDI.