I personally use DBDesigner which is free and can reverse engineer your Oracle database. You'll find it here. However, you'll notice that it is aimed at MySQL, so the Oracle datatypes will be mapped to MySQL datatypes... If you don't plan to use it to re-create objects in your Oracle database, it will be sufficient IMO.
HTH & Regards,
ORA-000TK : No bind variable detected... Shared Pool Alert code 5 - Nuclear query ready .