Below we will publish default passwords we encounter.
General (vendor):
3Com: admin/admin
Belkin: admin/admin
BenQ: admin/admin
Grandstream: admin/admin
D-Link: admin/admin
Digicom: user/password or admin/michelangelo
Linksys: admin/admin
Netgear: admin/password
Sitecom: sitecom/admin
Thomson: user/user
US Robotics: admin/admin
Zebra: admin/1234
Specific (device):
Brother MFC-L9570CDW: initpass
Brother LP844: admin/1234
Panasonic KX-UT133NE: admin/adminpass