Making a custom error page helpful for developers

Sometimes (for apps on an intranet), on the custom error page I put something like this:

@model System.Web.Mvc.HandleErrorInfo

@if (Model != null)
    <p>@Model.Exception.GetType().Name<br />
    thrown in @Model.ControllerName @Model.ActionName</p>
    <p>Error Details:</p>

Since you're leaking details to the outside world I don't recommend it for all sites. Can also make sure it's only shown to some users.

<customErrors defaultRedirect="~/Error/HttpError" mode="On">
  <error statusCode="404" redirect="~/Error/NotFound"/>

I use Elmah.axd to log errors. See elmah — make sure it's secure!