Website Monitoring / Downtime Notifications

[thegingerkid]

Hi, I'm just wondering what services people recommend for basic website monitoring. I don't need anything fancy; I was just hoping for a free or extremely cheap service that sends an email or otherwise notifies you when your site is down. I don't need a lot of in-depth reports or anything like that; just trying to get a general idea of my sites' uptime for now so that I can get an idea of how they're performing. Any suggestions? Thanks!