What do you use to monitor your websites?
barmstrong: I use monit on my linux boxes.It requires some setup but the big advantage of this is that it can not only tell you when your site is down, but sometimes ACTUALLY FIX IT by restarting nginx or whatever you need it to do.This is something a monitoring service can't do since they don't have access to your box.  Of course it's not going to be able to fix all situations that could cause downtime, but if it hits a scenario you anticipated it will.