pam_af
This PAM module is intended to prevent brute-force attacks on services like SSH or telnet. It maintains internal counters, and can execute pre-configured actions when failed attempt's count exeeds limit.
Current release is 1.0alpha. It's also the first public release.
It's tested on FreeBSD 4.x/5.x/6.x/7.x, RedHat Linux ES 4 and SunOS 5.10/5.11 x86. Probably, it will work on other platforms too.