...
no-ip.com
easydns.com
sitelutions.com
dnsomatic.com
ipv6tb.he.net
tzo.com
dhis.org
two-dns.de
www.dnsdynamic.org
dnspark.com
regfish.de
www.ovh.com
joker.com
system-ns.com
changeip.com
dnsexit.com
nsupdate.com
loopia.com
domains.google.com (requires SSL bridge, like stunnel)
duckdns.org
di.fi
ddnss.de
dynv6.com
selfhost.de