Splunk can get pricey if you have a lot of data coming in but there is no substitute, it is powerful.
If you are looking for free options, syslog-ng is one, you can also look at ELSA (open-source, similar to Splunk)
With syslog-ng, you can install a front-end such as logzilla or loganalyzer.
You really need to figure out what you want to capture first before choosing a syslog server, splunk is amazing but it might be overkill..