PHP does not lack for functions, especially for common items such as strings and dates. It is worth your while to bookmark the following chapters in the PHP Manual:
Strings at http://www.php.net/manual/en/ref.strings.php
Date/Time at http://www.php.net/manual/en/ref.datetime.php
In addition to keeping up with functions as they are added to PHP, the user-contributed notes for each function often offer solutions to various programming tasks that you might find useful as you build your own applications.