Great Syslog Target
On top of alerting we also track when certain accounts like domain admin.
Great for centralizing all your windows machines. You can flag certain events to trigger different actions of your choosing.
A bit overwhelming when you first add your server in bulk.
Great Log Management Suite
I loved how easy this software was to configure. I had all my logs pointed to it and flowing nicely in no time at all. It makes it very easy to look at your data and get a grasp of what is happening on your network.
It was a little costly compared to some of the alternatives out there. There are some good open source options out there.