Although there is a "Something Useful" topic it really isn't that uhhmmmm.... useful :)
http://www.php.net/manual/en/language.variables.external.php
Note:
The magic_quotes_gpc configuration directive affects Get, Post and Cookie values. If turned on, value (It's "PHP!") will automagically become (It's "PHP!"). Escaping is needed for DB insertion. See also addslashes(), stripslashes() and magic_quotes_sybase.
http://php.net/manual/en/debugger.php
Nothing useful in here.
http://php.net/manual/en/security.database.sql-injection.php
Full of ....
http://php.net/manual/en/language.variables.scope.php
Can we burninate the global keyword by now? At least it deserves a big fat warning.
http://www.php.net/manual/en/userlandnaming.tips.php
Nice tips going on here... ;-)
http://php.net/manual/en/pdostatement.fetch.php
Make examples readable
http://php.net/manual/en/function.include.php
Stop it with the globals already. People might think it is the next cool thing.