DD-WRT

(These were contributed by a user… thanks! Please let us know if these need updating.)

DD-WRT uses inadyn so the settings are:

DDNS Service: Custom
DYNDNS Server: updates.dnsomatic.com
Username: 
Password: 
Hostname: all.dnsomatic.com
URL: /nic/update?

This useful post on the DD-WRT forums may also help.