Website Uptime Monitor Service is a really nice simple service to monitor websites for free, No registration or signup is required, just put the site url, email and start monitoring. Few other features they plan to offer.
1. Site/Web Service Monitor
2. Email Alerts
3. Weekly reports
4. Checkout site uptime status anytime
5. SEO & Social Media coverage on Twitter, G+, FB, Pinterest, Blogger, Reddit for 95+ percent uptime!
They also have Android, iOS, Window's Mobile Apps also their site is compatible with all major smart phones.
Here is their website...