Firstly I'd like to agree with LokiDBA, Steven Feuerstein's O'Reilly series is excellent, I don't know of anyone who has bought them and been disapointed (Although I suppose there can always be a first). The other thing I would say is that if your after a book on tuning, which at the end of the day is something we all end up doing, Guy Harrisons book Oracle High Performance Tuning is, IMHO, the only book worth buying.