Arecont Vision
Arecont does not have a default password, but you can reset it to factory settings. Follow these steps

1-Access the camera's web interface by typing the IP in your web browser.
2-Under the Administration or System tab, click on Restore to Factory Default.
3-Once the camera reboots, all settings on the camera will be restored to factory default

AXIS
For an old system:
Username: Root
Password: Pass
IP Address: 192.168.0.90

But new generation AXIS cameras have a resetting sequence

BOSCH
For old models:
Username: service
Password: service
IP Address: 192.168.0.1
For new models:
You can reset the camera by pushing the reset button for about 7 seconds. Or you can reset the NVR by removing the battery on the mainboard (not recommended, at your own risk)

DAHUA
Username: admin
Password: admin

GEOVISION
Username: admin
Password: admin
IP Address: 192.168.1.108

HIKVISION
For old models (before firmware 5.3.0)
Username: admin
Password: 12345
IP Address: 192.0.0.64
For new models, you can reset the password via SADP tool. Please click the link below and follow the instructions on the pdf file
Hikvision password resetting guide

LTS Security
Username: admin
Password: 12345 or123456
IP Address: 192.0.0.64
For platinum models please click the link below for pdf file.
LTS platinum series password reset

Messoa
Username: admin
Password: 1234 or model number of camera or 
IP address: 192.168.1.30

Speco
For old models:
Username: root or admin
Password: root or admin
For new models:
Username: admin
Password: 1234
IP Address: 192.168.1.7

Vivotek
None. You can choose your own password after setup. If you want to reset it
1-Press and hold down the reset button for at least 1 minute
2-Power on the camera until the red light flashes rapidly
Now your camera is back to factory default without any password.

For other brands usernames and passwords please see below