Here is a CLR UDF I prepared for "Inside SQL Server 2005: Query Tuning and Optimization" (which I modified from the version presented in "Inside SQL Server 2005: T-SQL Querying" to better support NULLs):

[Microsoft.SqlServer.Server.SqlFunction(IsDeterministic=true)]
public static SqlString sqlsig(SqlString querystring)
{
    return (SqlString)Regex.Replace(
       querystring.Value,
       @”([\s,(=<>!](?![^\]]+[\]]))(?:(?:(?:(?:(?# expression coming
       )(?:([N])?(')(?:[^']|'')*('))(?# character
       )|(?:0x[\da-fA-F]*)(?# binary
       )|(?:[-+]?(?:(?:[\d]*\.[\d]*|[\d]+)(?# precise number
       )(?:[eE]?[\d]*)))(?# imprecise number
       )|(?:[~]?[-+]?(?:[\d]+))(?# integer
       )|(?:[nN][uU][lL][lL])(?# null
       ))(?:[\s]?[\+\-\*\/\%\&\|\^][\s]?)?)+(?# operators
       )))”,
       @”$1$2$3#$4”);
}