Revison 1
This is a faily simple function to validate a URL being passed into your scripts. It will allow for http, https, and ftp. The beginning www. of a URL is optional as well. It will also validate if you have an IP address in place of the domain name. I'm sure this can be improved upon as this is my first attempt at regular expressions but it has worked good for me so far. Please comment or improve if your able.

Thanks!