V$SYSSTAT Statistics such as the amount of data changed and the number of transactions executed.
V$SQL The actual SQL commands recently executed, how many time it was executed and how much CPU time it took.
V$FILESTAT The number of reads and writes per file, and time spent on disk I/O.
V$DATAFILE Lists the file number and name for each DB file.
V$DATABASE General information about the database
V$DBFILE Shows file name to numbers
V$PARAMETER Shows all the initializatino parameters and their current values.
V$SGA Summary statistics for the use of space in the SGA.
V$SESSION This view lists session information for each current session.
V$SESSTAT This view lists user session statistics.
V$SESS_IO This view lists I/O statistics for each user session.
V$SQLTEXT This view contains the text of SQL statements belonging to shared SQL cursors in the SGA.
V$SESSION_WAIT This view lists the resources or events for which active sessions are waiting.
V$OBJECT_DEPENDENCY This view can be used to determine what objects are depended on by a package, procedure, or cursor that is currently loaded in the shared pool. For example, together with V$SESSION and V$SQL, it can be used to determine which tables are used in the SQL statement that a user is currently executing.
V$LOCKED_OBJECT This view lists all locks acquired by every transaction on the system.
ALL_TABLES all tables accessible to the user
ALL_TAB_COLUMNS These views describe the columns of tables, views, and clusters in the database.
ALL_TAB_COMMENTS These views display comments for tables and views. Comments are entered using the COMMENT statement.
ALL_TAB_STATISTICS These views contain optimizer statistics for tables.
ALL_TAB_COL_STATISTICS These views provide column statistics and histogram information extracted from the related TAB_COLUMNS views.
USER_ERRORS Displays the errors found in views, stored procedures, and other objects.