Howdy,
Granted my needs are different from many here (all my work is non-commercial). But I find awstats to be a great stats package.
I actually just copy the .log file from the server every now and then and then do the processing with awstats on my local system (although awstats can also run on the server). My local system is a p3-500/win98 + cygwin and awstats performance is very good.
Another nice feature: awstats has a GPL or similar license (aka free!)
Peace,
David