For some of the sites I work on, that are either personal projects, or small, where I'm not going to setup Nagios, Monit, or some other internal or serious solution, I've been looking for monitoring services. What I've found, and signed up for (all of these), and will compare over the next few weeks are:
Have others to recommend? Please do tell. Note, they basically have to be free, or super cheap (which for me right now translates to maybe a couple bucks a month if, and only if, they are providing something more than simple uptime watching and monitoring intervals 10 mins or less (less is great, most of the above range from 5-60 minutes depending).