These are some of the online resources I have used, or am familiar with, to assist with genealogy research.
This a surprisingly valuable source of genealogy data. Memorials are maintained by users, and the site allows for messaging between users to ask questions and suggest updates.
This is a powerful, free search site for multiple public record types. It does offer family tree services.
This is a free family tree service that allows others to see and connect to common trees.
Ancestry.com is well known. I did not use the genealogy research features, however our family did use the DNA service.