Plugin to check IP address against a blacklist held by www.checklog.in
This plugin was created to work with http://www.checklog.in to restrict access to your website or WordPress install if a user is on a blacklist or does not verify against a whitelist of allowed IP addresses.
The free version will check all users access to your WordPress site to see if their IP is on a blacklist. If it is, they will receive a warning screen instead of accessing your site. Once shown, the details will be stored in their session so a new call to the remote database is not needed for every page call.
A paid version is also available which will email you when a user attempts to access your wp-login.php script (i.e they try to login to WordPress). They will receive a pending notification until you approve the IP address by clicking in the link in the email. Signup for a months free trial at http://www.checklog.in and see if it's right for you.