Answer by Nava Carmon for URL Validation function improving

Well, I found something on Microsoft site and with slight changes it's the best expression so far:

@"(?:[A-Za-z0-9!#$%\\&'*+/=?\\^_`{|}~-]+(?:\\.[A-Za-z0-9!#$%\\&'*+/=?\\^_`{|}"@"~-]+)*|\"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\"@"x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")@(?:(?:[A-Za-z0-9](?:[A-Za-"@"z0-9-]*[A-Za-z0-9])?\\.)+[A-Za-z0-9](?:[A-Za-z0-9-]*[A-Za-z0-9])?|\\[(?:(?:25[0-5"@"]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-"@"9][0-9]?|[A-Za-z0-9-]*[A-Za-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21"@"-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])";