Some things that could make ASP.NET MVC 4 Web API even better

gistfile1.cs

// this offends my coding sensibility

public Contact GetContact(int id)
{
    Contact contact = _repository.Get(id);
    if (contact == null)
    {
        throw new HttpResponseException(HttpStatusCode.NotFound);
    }
    return contact;
}

// most of it could become a extension method

public static T VerifiedToExist<T>(this T it)
{
    if (it == null)
    {
        throw new HttpResponseException(HttpStatusCode.NotFound);
    }
    return it;
}

// so the action would become

public Contact GetContact(int id)
{
    return _repository.Get(id).VerifiedToExist();
}