Well, I've been using this one: statcounter for a year or two. I like it. It counts stats and graphs them, but it also includes the searches that have brought people to your site - and, this is the part I really like, you can click back and see the actual search results as they looked for these folks so you can see where your site came up and what other sites they also saw as competition. Even better? It's free. You can see where they were from, what browers they were using etc.
It'd done with code generated to put on each page of each site you have. If you want to give clients, if you have clients, the chance to see only their stats you can. You can even set it up so that your ip address is not recorded in the stats you are tracking, as you are the one most likely to be visiting time after time.
[edited by: mona at 8:38 pm (utc) on Mar. 12, 2007] [edit reason] no urls, please - thx! [/edit]