I'd vote for pointing them at a feed service. You can sign up for Feedburner, only takes like a minute to do so and just have Feedburner pull your RSS. That way visitors to your site have the option to use what service they use. (ie My Google, My Yahoo, etc.)
Feedburner has a plug in themselves that can be added to your WP RSS feed but I don't like it. Takes it over completely and those who just want to grab the feed themselves get redirected to feedburner. I'm not cool with that.
Another method you can use is a page updating service. I actually run one myself and would not feel comfortable pointing you in the direction of any. A simple google search for 'update notification' pulls up a few links directly to them as well as pages that use services like these. (ie follow the links to the service and signup your own site.) If you go that route, then all you would have to do is provide a link in your links sidebar that says something like "Update Notification" and point them at the service.
Hope this helps,