important views in oracle database

Object related
dba_tables,
dba_views
dba_packages
dba_synonyms
dba_functions
dba_sequences
dba_triggers

roles related
dba_roles
dba_role_privs
dba_sys_privs
dba_tab_privs
role_role_privs

System related
v$backup
V$controlfile
V$log
V$archived_log
v$archived_gap
v$recover_file
v$session
v$session_longops