It depends on your needs. If, for example, you're running a data center and are mostly concerned with real-time alarming, then you might want to look at Avicode. It's very capable, but can be pricey.
If, on the other hand, you're supporting desktop applications or logs from remote systems, or are more concerned with offline log analysis then you might take a look at Gibraltar. It provides a nice combination of logging, log management and log aggregation/analysis capabilities. But, to be honest, I'm a bit partial -- I'm one of the Gibraltar developers.
