AT&T
http://www.att.com/speedtest/

CHARTER
http://speedtest.charter.com

CENTURYLINK
http://speedtest.centurylink.net
(redirects to http://spdtst-dlls.tx.centurylink.net/)
internethelp.centurylink.com/internethelp/zam-speed-test.html (redirects to http://internethelp.centurylink.com/internethelp/speedtest-q2.html)

COMCAST
http://speedtest.comcast.net

FAST
https://fast.com/

HUNTER
http://speedtest.hunterfiber.com

SPEEDTEST.NET by Ookla
speedtest.net/

SPEAKEASY
speakeasy.net/speedtest

VERIZON
speedtest.verizon.com (redirects to http://my.verizon.com/services/speedtest/)
speedtest.verizon.net (redirects to http://my.verizon.com/services/speedtest/)

ZDNET
http://www.zdnet.com/broadband-speedtest/