None of the other answers worked for me so I wrote my own solution:
As of Oracle 11g.
Replace USER with the desired username
Granted Roles:
SELECT *
FROM DBA_ROLE_PRIVS
WHERE GRANTEE = 'USER';
Privileges Granted Directly To User:
SELECT *
FROM DBA_TAB_PRIVS
WHERE GRANTEE = 'USER';
Privileges Granted to Role Granted to User:
SELECT *
FROM DBA_TAB_PRIVS
WHERE GRANTEE IN (SELECT granted_role
FROM DBA_ROLE_PRIVS
WHERE GRANTEE = 'USER');
Granted System Privileges:
SELECT *
FROM DBA_SYS_PRIVS
WHERE GRANTEE = 'USER';
If you want to lookup for the user you are currently connected as, you can replace DBA in the table name with USER and remove the WHERE clause.