Here is a dump of my favourite regex samples.

<?php  
// Replace Esperanto X notation user input with accented characters.  
$value = 'cxaro auxto sxati igxi'; // A string to test  
$patterns  = array(   '/sx/','/cx/','/gx/','/jx/','/ux/','/hx/','/Sx/','/Cx/','/Gx/','/Jx/','/Ux/','/Hx/');  
$replacements = array( 'ŝ',   'ĉ',   'ĝ',   'ĵ',   'ŭ',   'ĥ',   'Ŝ',   'Ĉ',   'Ĝ',   'Ĵ',   'Ŭ',   'Ĥ');  
$value = preg_replace($patterns, $replacements, $value);

echo $value;  
?>

<?php  
// Scrape movie quotes from a web site.  
$url = 'http://www.rottentomatoes.com/m/gone_with_the_wind/quotes/';  
$regex = '/<span class="line">(.+?)<\/span>/';  
$data = file_get_contents($url);

preg_match_all($regex,$data,$match);  
//print_r($match);  
// The array is in 2 parts. We just need the second part, $match[1]  
$quotes = array_rand($match[1],1);  
$quote = $match[1][$quotes];  
?>