The worst time for a webmaster is when they login to their computer and find that his/her site or blog’s server is down. I was just casually surfing and found a great site which can easily track up time of multiple sites together.

You can easily add multiple number of sites to monitor ( maximum 50 sites ) into your account and monitor them. You will keep receiving updates of your sites or blogs via E-mail, If you are in America you can also receive updates via SMS.

Link : Are my sites up?