Stumbled upon the best free stat counter I've ever seen. Blows away the popular sitemeter and all the rest. -- statcounter.com
(it's not a WP plugin -- it's the type where you plug some code into your page and their server tracks your site's activity through that.)
Loads of features, check out the demo!
Worked great for me in wordpress and it's XHTML valid (unlike many other stat counters). Can choose from a few different icons for the counter, or make it totally invisible -- no gaudy mandatory graphics. Ability to exclude your own IP (or as many as you want) from the count. Lots more.
I'm not affiliated in any way -- just a heads up to everyone here. Go check it out yourself.. Simple, clean, easy, free and loaded with features :)