Here is a bare minimum of the service accounts that I have used for the SharePoint 2010 farm:
SQL Server service account
Setup user account
Application pool account
Service managed account
Default content search access account
Automating SharePoint 2010 with Windows PowerShell 2.0 sheds the light on what service accounts are necessary to build a 2010 farm:
"Farm account" - (also reffered to by the SharePoint Configuration Wizard as the Database Connection Account). will be used as the central administration site Application Pool identity as well as the SharePoint Timer Service (SPTimerV4) identity.
Gary Lapointe strongly suggests to user another "Setup SharePoint" account which should be in the Web server local group "Administrators" and should have "dbcreator" and "securityadmin" roles on the SQL server.
You may need to modify the group membership for the farm account in order to start User Profile Synchronization Service
UPDATE: Todd Klindt has an excellent article where he presents his view on what accounts are needed for SP Farm 2010: Service Account Suggestions for SharePoint 2010