Since domain names are registered, we can learn a certain amount about them. A WhoIs lookup service will show us a record that will usually tell us, among other things:
A number of companies offer these searches for free; doing a search for "whois lookup" will retrieve several on the first page. Most will work for common top-level domains. (Click the image on the right for an example.)
Another strategy is simply to enter whois followed by a domain name into a Google search box. The first result will be a report that gives information about the site, including a whois record (scroll down to see it).
You can also use the URL and domain name to find out which sites link to a certain page or website. This way you can learn about the site's "network"—what kind of a crowd thinks it is useful. Are they all of the same political or ideological slant?
A great tool for this is Yahoo's Site Explorer. This tool allows you find out which pages link to a particular page or to an entire website. To use it, just enter the site's domain name and click the "Explore" button. Then, click "inlinks"; you can also choose whether to see pages that link to one particular page or to the website as a whole (click the image below to see an example).
You can also find inbound links by typing link: followed by the domain name or URL into a Google or Yahoo! search box.