Service Uptime is a website monitoring service that checks your website at regular intervals and notifies you via Email or SMS if it becomes unavailable.
The following is the list of the geographical monitoring locations:

Brisbane, Australia
Quebec, Canada
Florence, Itlay
Tokya,Japan
Amsterdam, Netherlands
California, USA
Florida, USA
New Jersey, USA
Texas, USA
Stratford, UK
Singapore

You can visit them at: www.serviceuptime.com.

Hyperspin is a website monitoring service that checks your website at regular intervals and notifies you via Email or SMS if it becomes unavailable.
The following is the list of the geographical monitoring locations:

Seattle, Washington, USA
San Jose, California, USA
Dallas, Texas, USA
Ashburn, Virginia, USA
Chicago, Illinois, USA
Hamilton, Ontario, Canada
Maidenhead, Berkshire, UK
Amsterdam, Netherlands
Singapore
Brisbane, Queensland, Australia

You can visit them at: […]

Site24×7 offers offers web application and DNS server monitoring to your website at regular intervals of time and alerts you if it is down. It also checks web page content, web page defacement and providers website performance tracking.
It notifies the users through email, SMS and RSS alerts if your site is down. It also provides […]

Host-Tracker is a website monitoring service that checks your website at regular intervals and notifies you via Email, ICQ, GTalk or SMS if it becomes unavailable.
The following is the list of the geographical monitoring locations:

Brisbane, QLD, Australia
Porto Alegre, Brazil
Hamilton, Ontario, Canada
Montreal, QC, Canada (3)
St-Leonard, QC, Canada
Poitiers, France
Berlin, Germany
Erfurt, Germany
WanChai, Hong Kong
Tehran, Iran
Amsterdam, Netherlands
Schiphol-Rijk, Netherlands
Moscow, Russia […]

SiteUptime is a website monitoring service that checks your website at regular intervals and notifies you via email or SMS if it becomes unavailable.
The following is the list of the geographical monitoring locations:

New York, USA
San Francisco, USA
Chicago, USA
London, UK

You can visit them at: www.siteuptime.com.