*****************
** 10g
*****************
SQL> select username,password from dba_users
2 where username in ('SCOTT','SYS');

USERNAME PASSWORD
------------------------------ ------------------------------
SYS 6F1C6AF6DF44BC28
SCOTT F894844C34402B67

*****************
** 11g
*****************
SQL> select username,password,password_versions from dba_users
2 where username in ('SCOTT','SYS');

USERNAME PASSWORD PASSWORD
------------------------------ ------------------------------ --------
SYS 10G 11G
SCOTT 10G 11G

PASSWORD_VERSIONS => Database version in which the password was created or changed.

至于加密后的密码，仍可以在USER$视图中找出来。
SQL> select name,password from user$
2 where name in ('SCOTT','SYS');

NAME PASSWORD
------------------------------ -----------------
SCOTT F894844C34402B67
SYS 8A8F025737A9097A

Oracle 11g中还能轻易找出当前数据库中使用默认密码的用户:
SQL> select * from DBA_USERS_WITH_DEFPWD;

USERNAME
------------------------------
DIP
MDSYS
WK_TEST
CTXSYS
OUTLN
EXFSYS
SCOTT
DBSNMP
MDDATA
ORDPLUGINS
ORDSYS
XDB
SI_INFORMTN_SCHEMA
WMSYS

已选择14行。