Down for everyone or just me? (http://www.downforeveryoneorjustme.com/) is a popular website that checks if another website is down. For example, if you can't access Yahoo, Google or YouTube, you can use this tool to see if there is something wrong with the website or if its just on your end.
Ironically enough, when I tried to use it tonight to check Wiredfan, Down for everyone or just me? is down. LOL. I had to use other similar websites to check.