If you are a C# programmer, chances are that you are using Enum.Parse somewhere in your code. You must be knowing that Enum.Parse throws an exception if you pass an object which is not a member of the enumeration. There are two ways in which you can handle this exception. You either adorn the call to Enum.Parse with try-catch block or use Enum.IsDefined.
I like the latter for obvious reasons. Enum.IsDefined checks if the given object is a valid member of the given enumeration type. If it is, returns true. false, otherwise. So simple, yet so powerful.
Use it and admire it.