mon.itor.us is a free uptime monitoring service for your website.
It can perform many different tests, from http to ftp and imap.
If you insert in your site a code snippet provided from mon.itor.us, you can also have a visits traffic report, but the site has a lot of services available.
When you register, you can have your alerts delivered also to your msn messenger / GTalk / ICQ account (you need only to add to your buddy list a new contact).
But the one very thing that caught my attention is the possibility to access those reports and data from Windows Mobile devices: simply reach http://mobile.mon.itor.us and read all the fundamental site stats on the go. Works!
Here's a screenshot of the mobile web page: