Oracle Performance & DB Management Links
If you have an oracle support contract, then you should have a metalink account. Make use of it.
Contains documentation, bug reports, patches, etc.
You may have to sift through some 'extra' info (some people call it junk), but many answers can be found there.
If you can't find your answer, you can always post a question to a forum, or log a TAR.
The premier Oracle guru.
If Tom doesn't have an answer to your question then most likely, no one does.
A wonderful database management tool.
Cross platform (runs on any OS that supports java)
Supports virtually all major databases (Oracle, SQL Server, DB2, Postgres, MySQL, Informix)
ITtoolbox for Oracle Knowledge Base
Content, community, and service for Oracle professionals.
Providing technical discussion, job postings, an integrated directory, news, and much more.
A wealth of scripts, tips, and performance tuning information.
Statspack and bstat/estat analysis tools.
Also available is an excellent performance profiling paper by Anjo Kolk. (free registration required)