On the Dreamincode.com forum there's an interesting approach mentioned for security login forms from brute-force attacks using a queueing system rather than the usual real-time requests.

Login forms in online systems are often easy targets for brute-force attacks; attacks designed to go through all possible values (or at least all probable values) for a password to "guess" a correct one. Securing your forms from such attacks is important, but it can be tricky to do in an effective manner without adversely affecting the user experience of your normal user. The method I am suggesting in this article is that of queuing login attempts in an effort to limit how many attempts an attacker can execute per second. [...] So, how do we implement this in PHP?

He suggests using a MySQL-based queueing system (but it could easily be replaced with one of the *MQ types) that tracks users versus login attempts. He's put together a library that handles the storage and login attempt management. He takes some time to explain the functionality of the class and how to put it to use.