Links
Even though the Internet is an absolute help in finding information on Oracle the sheer number of sites and dubious quality of them merrits listing the oracle sites I find the most usefull.
Oracle-L Discussion Forum
The OAK Table
ss64 (list of command syntaxes etc)
Oracle Base (Tim Hall's site)
Miracle A/S
Jeff Hunter's site
Jonathan Lewis's site (optimizer internals)
OraFAQ (code examples)
OraRSP performance tool (opensource)