Here are some of my favourite links:
Automation Direct – They have their own line of affordable programmable logic controllers. I bought everything from them to build my Programmable Logic Controller Trainer Panel. They’re based in the USA and have a great variety of automation parts.
Dipmicro – They’re based in the Niagara Falls area on both sides of the border. They’ve got a good variety of components. I like them a lot because their prices are very reasonable, including their shipping rates.
Dirt Cheap Dirty Boards – An inexpensive PCB manufacturer.
Robot Shop – This site caters mostly to the mobile robotics crowd so I don’t buy from them very often. What I have purchased from them so far has been of good quality, which is something that can vary at times from cheap sources. Shipping is fast.
Sayal Electronics – This is the only physical electronics store I regularly go to. Their prices aren’t really cheap but they’ve got a great inventory of electronic components and other items I’d rather buy in person, like solder and flux. It’s great to go there if I feel the need to get a part quickly or even just walk around to get ideas.
Tutorials and Reference
Adafruit – The Adafruit Learning System never stops growing. Lots of information and tutorials to be found!
Instructables – I have used articles on Instructables to get inspired and started on some projects. It’s great to see how other people go about making things!