Know when your site is down before the customer (or your boss) tells you! Monastic is a totally free service to monitor your sites uptime. Some of the features are
Website monitoring made cool:
Get an email when your site goes down
Get an email when it goes back up
Read statuses via RSS or Mac & PC widgets
Fun, easy and elegant user interface
Up to 100 websites monitored
NEW! Support for https and port numbe
Currently Montastic checks your sites at least 6 to 20 times a day. They are working on upgrading their capacity to meet demand and achieve a 10 minute checking interval goal.