Analog http://www.analog.cx/ is a flexible, fast, and free web log analysis program. It runs on just about anything.
I compiled several versions of Analog (the plain command-line version) for Mac OS X (and Darwin, although I don't know if anyone ever ran it under Darwin). Since then, the Fink http://fink.sourceforge.net/ project has taken over my port; Fink can download, patch, and install Analog automatically ("fink install analog" once fink is installed).
Additionally, there's a more Mac-like Carbon version maintained by Jason at summary.net.
I have also created a simple tool called Logwrangler to facilitate managing stats for multiple sites; it can control Analog, Report Magic, and DNSTran, and generate a summary table for multiple sites.
The official Analog site is at http://www.analog.cx/.
Warning: When Analog does significant numbers of DNS lookups under Mac OS X, the Mac OS X resolver tends to crash (it doesn't affect the rest of the system). I've reported this to Apple as bug #2692867; it's still broken as of April 2003 (3 years later).