I actually released a plugin a few months back called Naughty Monkey that you might find useful Jeff. The name is meant to be more humorous than descriptive, so here's the gist of what it does. The premise is that you've changed the default administrator account to use something besides "admin" (the plugin checks that you've done this and doesn't operate if the "admin" account still exists). If a user tries to log in with the "admin" user account, their IP is automatically added to a list of banned IPs. Here's a link if you're interested.

http://www.itsananderson.com/plugins/naughty-monkey/