orielly books on plsql
oracle 24X7 tips and techniques by venkat devraj
oracle performance tuning tips and tricks by rich mimec
oracle advanced pl/sql programming by urlike schwinn
oracle backup and recovery guide by rama velpuri
oracle annotated archives by kevin looney and rachel carmiceal
oracle dba tips and tricks by sumit sarin
most of my dba skills were honed from these places hope it
will help you too.
the official web site of ORACLE.Which has many links which will guide you to become a good dba.
and the second is http://www.dbasupport.com where you can have a good exposure to experience and help to solve the real time problems.This is very important to be a ACE DBA.
If you go into many web sites you will really loose the focus and waste of time in addition.Some sites may help you to pullout some questions banks useful for OCP exams.
What i simply could suggest you is have a atleast initial DBA class instructor course .Its very important you understand the Oracle Architecture to become a succesful DBA or if you can have a good guide as a friend to help you such as a real time DBA in your self studies then fine go ahead.
For more help post your doubts in this forum.
Wishing you all the best and success for your new endeavors.