To know your public ip. It shows location and other details too.
http://whatismyipaddress.com/For checking nameservers, mx record, A record, PTR record and other DNS details.
http://www.intodns.com/Example:
http://www.intodns.com/randeeppr.meFor checking the accessibility of your ip address or url. It gives ping results from many parts of the world.
http://www.just-ping.com/For checking the domain details such as owner of the domain and contact details.
http://www.whois.sc/Example:
http://whois.domaintools.com/randeeppr.meTo check whether your ip is blacklisted or not
http://www.mxtoolbox.com/blacklists.aspxTo check the loading time of the url from different parts of world
http://alertra.com/spotcheck_doTo check the domain propagation, NS, MX, A Record etc from different parts of the world at the moment.
http://www.whatsmydns.net/To check the cpanel license is expired or not
http://www.cpanel.net/apps/verify/To paste the error log and make a link to exchange
http://pastebin.com/