Login LockDown is a WordPress Plugin which locks a wordpress account when a hacker failed to login via the login form for WordPress more then 3 times. He has to wait for 1 hour before he can try to login from the same IP range with the WordPress login form. This plugins prevent brute force password discovery where the hacker uses a bunch of common passwords to try to login to your account.
You can manually set the Max Login Retries, Retry Time Period Restriction (minutes), Lockout Length (minutes), Lockout Invalid Usernames?, Mask Login Errors?, and Currently Locked Out.
Download Login Lockdown at http://wordpress.org/extend/plugins/login-lockdown/