Uptime Service Recommendation

Try Pingdom: http://www.pingdom.com/
I've used some of their other tools but not yet their uptime and performance monitoring. I'd be interested to know what you think of it.

Randall Knutson (Levelten Design) reviewed Showslow.com which may be of use for uptime monitoring:

"Show Slow is an open source tool that helps monitor various website performance metrics over time. It captures the results of YSlow, Page Speed and dynaTrace AJAX Edition (webpagetest.org) rankings and graphs them, to help you understand how various changes to your site affect its performance."

http://www.leveltendesign.com/blog/randall-knutson/showslow-monitor-your...

I came across this post while looking for a good monitoring solution.
After some testing, I decided to use Pingdom.
Why:
The price (with annual billing by far the cheapest I've found)
Scalable (I can add more checks whenever I want for $ 0,50 / site / month)
Look-and-feel: It has the best interface I've seen for this kind of service.
iPhone app: A good add-on
Custom domain for reporting: I can give my client their own url on my domain, e.g. http://uptime.flodo/nl/[client-string]
Desktop notifiers (Mac, the party and their own Windows notifier)

But most of all I like it that I can set the interval of the check to 1. 5, 15, 30 or 60 minutes for the same rate. Other services give you 7 5-minute-checks OR 15 30 minutes-checks etc.

http://pingdom.com
And an example of reporting on my custom domain: http://uptime.flodo.nl/389954 (Where flodo.nl is my own domain)