Brute Force attacks – What to do?…

During the last few months, my site has been – and still is – undergoing brute force attacks. It has become unavailable many-many times….

I use iThemes and Simple Firewall to try to prevent these attacks (and tried out many more such plugins…) but none of them provides optimal security.

My problem is that if I hide wp-login or wp-admin, users cannot login to their accounts to modify their listings if they need to do so. But http://www.mysite.com/wp-admin is an open invitation for brute force attacks…

I would appreciate to have any (ideally: proven) solution or idea to prevent brute force attacks on a site using Directory Press.

Thanx,
Attila