Canadian

Canada Drones: Your Canadian source for UAV gear! (Mississauga, ON)
CustoBots: Robot parts and kits, specializing in humanoid/walkers (Calgary, AB)
DigiKey Canada: Lots of electronics components
Dr. Robot: Wireless Robotics (Toronto, ON)
Future Electronics eStore: Lots of electronics components (Pointe-Claire, QC)
Gateway Bot Shop LEGO and Robotics – Classes, Workshops, Camps and BDAY Parties
Great Hobbies: Small Batteries (Edmonton, AB)
HVW Technologies: Canadian robotics source (Calgary, AB)
Plantraco Hobbies: Lithium Polymer Batteries and Chargers (Saskatoon, SK)
SOC Machines (North Vancouver, BC)
Solarbotics: Robotics Information and kits (Calgary, AB)
Robots in Search: Carries some Pololu stuff (Toronto, ON)
RobotShop.ca: Parts, Kits, & more (Montreal, QC)
Rouge Robotics: Small online store (Markham, ON)
R.P. Electronics: Electronics in the Lower Mainland (Burnaby, BC)
SMI Industrial Electronics (Langley, BC)
SpikenzieLabs: Arduino, parts, and more(Montreal, QC)

Other

Acroname: Parts and Kits
Active Robots (UK)
Budget Robotics: Affordable Robotics Parts
Junun.org: The Mark III Store – Inexpensive parts
Kronos Robotics: Parts, Kits, Useful Information
Lynxmotion: Good Quality robotics kits
MakingThings: Modular blocks for automation
NPC Robotics: Lots of useful stuff for larger (aka BattleBot) sized robots
Parallax: Your Basic Stamp Manufacturer
Pololu: parts, and these guys do custom laser cutting
Robot Directory: A collection of user submitted robots
Small Parts: Lots of small stuff that’s difficult to get
SparkFun: Many, many interesting electronic widgets and parts
SmartRobots: Beacon Navigation kits and Software
The Robot Store: Kits & everything robotic