PHPInclusion WordPress plugin allows you (admin only) to insert the content of a php file into your post/page with include(), require() , require_once() and include_once() functions.
Usage :
Copy & Past this code into your post or page :
[include:Path to your php file]
[include_once:Path to your php file]
[require:Path to your php file]
[require_once:Path to your php file]
Examples:
[include:MyPhpFile.php]
[include:MyDir/MyPhpFile.php]
More About PHPInclusion Plugin :
http://www.royakhosravi.com/?p=63