Montastic is a free site monitoring service based on Ajax and Ruby on Rails, that doesn’t suck, as their tagline goes. What it does is simple — it sends you an email when your site bogs down. Montastic hasn’t emailed me yet, but by just signing up with them I’m sure my sites are in pretty good hands. I know I can’t watch my sites 24/7, but Montastic can do that for me, for now.