When you consider buying a new domain, whether it is currently registered or not, it is useful to know it's history. There are three tools that can help you to find information on the history and ownership of a domain.
You can use HosterStats to discover which hosts a domain has pointed to in the history based on DNS settings. The DNS names can often be quite revealing in regards to which companies controlled the hosting, or if an internal DNS name is used you can often discover the corporate owners of a website.
The Wayback Machine Internet Archive periodically takes “snapshots” of how a website and individual web pages looked on a certain day in history. Whilst not every page will be captured and some less frequently than others you can usually find a few records at a minimum for each site. This can give you insight on how a website looked before an owner let it drop, how a company marketed themselves historically and if you're really bad at keeping backups, it can sometimes save your ass when a page is deleted but still recorded here!
This site is especially useful when a domain name is still registered as it allows you to lookup their WhoIs record. Inside you will usually find the contact details for the owners and administrators of any website and can get an idea of how long they have owned the site for. This site is very powerful when conducting marketing research and if you stretch to a premium subscription you can also pick up a lot of historical changes and cross reference other sites owned by the same people.
There are many tools that you can use to find out additional information about a domain name or website. Whether the site is still going or has been dead for years, there is often a wealth of information about its ownership and status at any given date in the past. The more you play with these tools the more creative ideas you will probably find your using the information.