Useful extended events objects

Name Columns
SQL Server 2008 R2
sqlserver.sql_statement_completed duration, reads, writes, cpu_time
SQL Server 2012
sqlserver.sql_statement_completed statement, logical_reads, physical_reads, row_count
sqlserver.sql_batch_completed duration
sqlserver.error_reported error, severity, user_defined, message
Name
sqlserver.session_id
sqlserver.sql_text
SQL Server 2012
sqlserver.session_server_principal_name

The full list of available extended event objects is available in the system catalog:

SELECT 
  o.name AS ObjectName
, o.object_type
, o.[description]
, c.name AS ColumnName
FROM sys.dm_xe_objects o
  LEFT JOIN sys.dm_xe_object_columns c 
    ON c.object_package_guid = o.package_guid
    AND c.[object_name] = o.name
ORDER BY
  o.object_type
, o.name
, c.column_id