So did you ever run into a website you questioned the authenticity on? Or did you ever want to teach students about evaluating online resources? Well Review and Judge (www.reviewandjudge.org) may be a pretty good resource for you.
Pretty simple too, you type in your webaddress, it takes a little while, and it spits out 3 ranking for indicators. They take into consideration the age of the site, the popularity, and the Google ranking. Obviously you can use those for what they are worth, as you still can manipulate some of these. Age, for instance, does not necessarily mean a site is reputable or not on its own, but taken together, this site will provide you and your students a starting point for judging the reputable status of a particular site.