A month ago I added BrowserMob to my toolbox. I’m sure I’m the last web-guy in the world to discover BrowserMob (or “Neustar Web Performance”, as of yesterday), but just in case you don’t know them either, it is an online service that provides availability- and performance-monitoring for websites and -applications.
Great stuff, really; create a simple script by providing a URL, choose what datacenters you want the test to run from, set the interval and there you go. After a couple of minutes you can start gazing at charts & reports or check your mailbox for alerts. You can create more complex tests using a JavaScript-based syntax or you can import Selenium-scripts (hello Selenium IDE for FireFox). The free account I started out with offers a substantial amount of pageviews/ month (40.000) that tests can generate.