To help diagnose issues or to show warnings on your network, OpenDNS owns, operates, and uses the following:

http://welcome.opendns.com - produces either

(o) www.opendns.com/welcome/ or
(i) www.opendns.com/welcome/oops/
(Indicates whether or not you are using OpenDNS right now.)

https://dashboard.opendns.com/ - Displays Dashboard news and Malware/Botnet warnings:
(o,i) Malware/Botnet status: OpenDNS has detected no [or some] evidence of malicious activity on your network... (when logged in).

http://internetbadguys.com/ - produces either
(o) phish.opendns.com/?url=www.internetbadguys.com = BLOCKED or
(i) internetbadguys.com = "only a demonstration site"

http://www.exampleadultsite.com/ - produces either
(o) blocked-website.opendns.com/?url=... = BLOCKED (if Nudity or pornography filtering is enabled)
(i) exampleadultsite.com = "only a demonstration site"

http://www.opendns.com/about/share/ - produces either
(o) The Live Preview buttons: "You're using OpenDNS - Sweet!"
(i) The Live Preview buttons: "OpenDNS - Get Started"

http://domain.opendns.com - Takes you to the Community Domain Tagging voting page
http://www.opendns.com/community/domaintagging/
http://domain.opendns.com/anydomain.net produces:
http://domain.opendns.com/anydomain.net = individual tagging and voting page.
(domain's existence not checked)

http://system.opendns.com/ - OpenDNS System Status Page - what's working.
http://208.69.38.170 - Reach System Status even if DNS services are not working.

http://www.phishtank.com/ - Nominate, vote, or check URLs for phishing status.