VS 2005 Cool Feature #2 - String.NullOrEmpty
This one is simple, it allows you to test for null or empty strings in one static function:
string s = null;
string s2 = string.Empty;
string s3 = "";
if (string.IsNullOrEmpty(s) && string.IsNullOrEmpty(s2) && string.IsNullOrEmpty(s3)) Console.WriteLine("Works");
This is more for convenience than anything else.