wp2syslog -- Global logging facility for WordPress (WPsyslog revisited)
A mini Time Machine... kind of. Great to get some vital data... to see how often people log in... or to trace errors due to plugin updates.
You can clearly see failed log ins and their IP addresses, in conjunction with fail2ban this has been a great addition to my blogs.
I found this useful because I hate debugging traffic especially if the IP and "user" operation is not correlated (I don't own the servers). Thanks! :-)