DNS Watch and Domain Tools are some examples of services that allow you to perform a DNS lookup. Google also offers its own domain name server lookup system called Dig.
Dig and DNS Watch are free services that allow you to look up various details linked to a DNS, such as domain name availability, IP addresses, name servers, and the creation and registration date.
You can also perform a DNS lookup yourself, using a command line interface such as CMD in Windows or Terminal in OSX. Using the nslookup command, entering the domain name as a parameter will yield its corresponding IP address. You can also perform a reverse DNS lookup by entering the IP address. This is particularly useful in the case that multiple domain names are associated with a single IP address.
In addition to its free DNS lookup service, DNS Watch offers several paid products, such DNS Changetracker, which can monitor any DNS for any changes 24 hours a day. It also offers a service to monitor the performance of your DNS, which tracks how quickly the DNS server responds to queries.
Domain Tools offers professional services that can be used to track domain name servers for monitoring the security situation of a DNS. The service can also be used to investigate online fraud or monitor your web portfolio.