I'm currently using New Relic's performance monitoring service. Works great so far, except that I'd like some things automated. I basically just get an email notification when performance is bad or my site is down. If the site is down, I'd like to try restarting the application server (killing the process if necessary, which it is sometimes). If that doesn't work after a period of time, try rebooting the whole machine... I even paid for PagerDuty, which can parse New Relic email notifications and call or SMS me with an escalation procedure for notifications. But it can't run scripts...
Seems like this would be a popular feature of any website monitoring tool... anything good out there?