Ancestry.Com : One of the most well known sites. Very little info free, most have fee.

CPRoots : Many various Sections, Surnames Exchange, Databases & Links. Free

Cyndislist : One of the oldest and best. Not so much data here but invaluable as a clearing house for many thousands of other sites to search. Free

Family Search : The genealogy section of the LDS Church. Vast database of information and records. Free

Genforum : Leave inquiries by name and search for other inquiries by name from others. Free

New England Ancestors : Not just for ancestors in New England, but all over.

RootsWeb : Vast databases. A very good site for submissions and searches of trees and databases.

U S Gen Web Project: A nationwide genealogy project to collect data. Has sites in almost all states and counties nationwide. Free.