Freelance Forums

http://www.alertra.com/ Is a very good and affordable service you can use to monitor your site. I've used their service and its very easy to setup and use.

Google Analytics is free and amazing!

I log browser, os, ip, url, and date for every page view of my sites and have built custom report forms to use this data.

Does Google analystics actually monitor your site though? I thought it just did some statistical analysis. This company service looks like it's going to inform you soon after your site goes down, sounds pretty useful to me!