http://regexlib.comThis site has a library of RegEx patterns. Many times you can find a solution to a RegEx quicker than you could create one.
If you wish to build your own or need to test them, you can get the "Regulator", which is a Windows app. It is integrated with RegExLib.com and makes it easy to obtain and test their RegEx patterns. Great utility!
http://royo.is-a-geek.com/ISerializable/DesktopDefault.aspx?tabid=27