Helpfule Regex - Regular Expressions in Salesforce.com

Post for later reference about regex

val = 'random string!@#$%^&*()_';

//AlphaNumber Only

val = val.tolowercase().ReplaceAll('[^a-zA-Z0-9]', '');

//AlphaNumber Only + Special characters

val = val.tolowercase().ReplaceAll('[^a-zA-Z0-9@$_.~\'-]', '');

system.debug(val);