This question is for IT Pros, and people who manage a company's infrastructure. Developers should see this related answer for tools geared for them.
What are your requirements for such a Event Log Managment solution? What do you currently, or do you hope to derive from such a system?
I found a related question that focuses on how an application should save to the eventlog, but this question is orthogonal to that. Here I'd like to what tools, reports, and surrounding alerts you want from a system that aggregates, and analyzes log files.
In an Enterprise setting this would undoubtedly include: Windows Event Logs, Firewall, Router logs, syslog, etc.