I have put this:
http://wordpress.org/extend/plugins/statpress/ on some of my smaller feeder blogs, just to test it. It's really simple, and does what I need it to do, which is counting hits, SE-hits and referrers.
I also used Wordpress stats:
http://wordpress.org/extend/plugins/stats/ - a good thing about this one, is that it registers which links your visitors click on
