There are a number of great sources where you can purchase components as needed, today I’d like to go through a few of the ones I’ve used and hopefully give you an idea of where you can go to get all the parts you’ll need for any project you tackle. This is by no means a comprehensive list but the below suppliers are where I source the majority of my parts.
Local
Buying local is typically the most expensive way to get parts but that is balanced out by the instant gratification you receive from walking into a store, giving them your money and walking out with your components. Though I wouldn’t recommend purchasing large quantities of parts in this way it is incredibly useful to have a store you can run to if you find yourself missing a specific piece you need to complete your project. Not to mention the right shop’s staff can be an excellent source of expert advice.
Radio Shack – I’ve read and been told that Radio Shack can be a good source of parts but unfortunately where I am located (In Ontario) we only have Circuit City which I have not had very much luck with. Typically their prices are extremely high and the selection is almost none existent.
Independent Stores – Independently owned electronics retailers are typically your best bet for a local parts supplier, if you can find one… Unfortunately due to competition with online retailers and the niche nature of their products these shops are getting harder and harder to find, but if you live in a large enough city have a look around and you may find something great. Typically you will pay substantially more than you would ordering parts online but you will be able to get the components you need without causing delays to your project.
Online
All Electronics – All Electronics was the first site I began ordering from and I’ve always had good experiences with them. They have reasonable costs and an easy to navigate site. Though they do not have as large a selection as some other suppliers this can actually be beneficial when your starting out, there is nothing worse than wading through a thousand different types of 10 ohm potentiometers just to try and find a volume control .
Jameco – Jameco is similar in scope to All Electronics though I’ve switched quite a bit of my business to them as I’ve found they stock a few more obscure parts (some CMos logic chips and the like) which I wasn’t able to find through All Electronics. My recommendation would be to try both these sites to get a feel for them and where both of there strengths lie.
Digikey – A moment ago when I mentioned wading through a thousand types of potentiometers… welcome to Digikey. I would recommend waiting until you are fairly comfortable with component types, manufacturers and specs. Often times without a specific part number for what you’re looking for you will end up sifting through page after page of near identical parts into oblivion. That being said if ever there is a part you can not find elsewhere or an IC too obscure to be widely available. Digikey will have it.