A couple weeks ago, I started using Mon.itor.us for uptime and response time tracking of my websites. They're free. They use a Netvibes-ish widgety sort of monitoring page where you can build custom graphs and charts for your sites. I'm pretty impressed so far. I tagged my various "External Monitors" (site response and uptime checkers) by the hosting provider, and I'll probably add tags for the software packages I use (Joomla, PHPBB, etc...) to do additional comparisons with their "External Report" feature, which can give you data by tag.