In case you don’t already know about it, Google Analytics is a free service that offers an amazing level of detail about access to your website, in an easy-to-use format. Here’s the “front page” of analysis for GBMINI, which I set up a week or two ago:
Josh Wardell introduced it to me (I think he’s been using it a long time), and I was impressed enough to try it immediately – you have to sign up at Google Analytics, add your website, then paste some supplied (Javascript) code in to every webpage, which is easy to do with WordPress since you can just modify the template header or footer.
Since it uses Javascript, it won’t work for people that have turned off such features in their browser – but it still gives impressive data, including average daily visits, most viewed pages, information on how visitors got to the page and where they went next, and location of the visitor (down to city detail for USA).
It’s intended for users of Google advertising features, and has loads of stuff I don’t use that helps figure whether people buy products or not! But for me, having an easy view of my websites is enough, and I love the price!
M&I / GBMINI 
I’ve been using it for 2 years. My website guy set us up. It is great to find out how people get to your site. Helps in advertising dollars!!
Ian, I too have been using it for a couple of years and find it pretty useful. The filtering allows you to exclude your own access from the stats and there are some great ways to follow up on where referrals are from and which articles are the most popular. The new benchmarking feature is kind of interesting.
I’ve been using this on and off for a few years and it works ok. currently using it on WRR, but it doesn’t track downloads or count iTunes as a user, so it’s not terribly accurate.
Otherwise I use awstats that site5 provides. I’ve compared it to other stats packages and it’s very good.