The following are a list of Regular expressions that I have either written or come across on other sites. This list will be expanded over time so check bak on this article.

Usage expression
Check email address [code]([0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9})[/code]
Check URL [code](ht|f)tp(s?)\:\/\/[0-9a-zA-Z]([-.\w]*[0-9a-zA-Z])*(:(0-9)*)*(\/?)([a-zA-Z0-9\-\.\?\,\'\/\\\+&%\$#_]*)?[/code]
UK Date dd/mm/yyyy [code](((0[1-9]|[12][0-9]|3[01])([-./])(0[13578]|10|12)([-./])(\d{4}))|(([0][1-9]|[12][0-9]|30)([-./])(0[469]|11)([-./])(\d{4}))|((0[1-9]|1[0-9]|2[0-8])([-./])(02)([-./])(\d{4}))|((29)(\.|-|\/)(02)([-./])([02468][048]00))|((29)([-./])(02)([-./])([13579][26]00))|((29)([-./])(02)([-./])([0-9][0-9][0][48]))|((29)([-./])(02)([-./])([0-9][0-9][2468][048]))|((29)([-./])(02)([-./])([0-9][0-9][13579][26])))

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An unbelievable source of expressions can be found at http://regexlib.com/DisplayPatterns.aspx
They even have a validator there.