Even if you can find the perfect part, sometimes you can't find anyone who is willing to sell you one. Here is some information on component suppliers.
These guys have huge catalogs and an immense selection of parts, yet are still willing to sell things in onseies-and-twosies to hobbyists who can't claim to be prototyping something that'll sell a million units next year. Digi-Key actually got its start in the ham radio market, selling digital keyers.
I (Wiml) find that Digi-Key is the place to go for digital stuff, microcontrollers, and the like. For discretes and analog parts, Mouser is usually cheaper and has a better selection. Neither company has a minimum order, but of course they do have shipping and handling fees which make small orders impractical.
I, myself (who?) appear to have found that Jameco is good for small quantities of a fairly common part. They don't have anything surface mount, though. For that stuff, I had to go to Digi-Key. I called up Digi-Key to see if I could alter an order I had just placed before it got fulfilled. My order was already far enough along that they couldn't stop it. I believe the phrase was "too far gone". That speaks well of their order fulfillment process. I hear Mouser should be in there too, but I've never had a compelling reason to use them.
http://www.alliedelec.com/Images/logo_allied.png Allied Electronics Honestly I'm not sure if this is a mid-size or large distributor (how are we to tell, anyway?) Allied tends to deal more with "heavy duty" electrical parts (wiring, relays, electromechanical, etc. . .) rather than electronics. However, I've noticed that they do have some suppliers that Mouser/DigiKey don't have in terms of electronics components.
http://www.newark.com/images/en_US/logo_nio.gif Newark My most recent "Newark in one" catalog is even thicker than my most recent Digikey catalog. (The "in one" motto and the swirly logo look identical to the Farnell logo. Is there some kind of connection?)
Newark usually has just about every odd semiconductor you might need in stock. Their shipping tends to be rather expensive, however (be prepared, as they won't give you a shipping quote until after you order, just like every other distributor), and they seem to really not like small orders, in my experience.
Newark InOne, Farnell InOne, and MCM InOne are all electronics distributors owned by the InOne Company.
http://www.jameco.com/wcsstore/Jameco/images/jamecoLogo.gif Jameco Jameco's catalogs have been getting fatter recently and their prices are good for common parts. Their Jameco ValueBrand parts are often much cheaper than the competition. (I have yet to notice the difference, personally -mdwebster) Jameco tends to focus on generic and older parts, where the giant supplier tend to focus on newer brand name parts. Jameco has a decent selection of cheap tools.
Radio Shack is OK if you need a common part NOW, but expect to pay probably 10 times the mail order price. In the past couple of years (2005-2006), I've noticed many Radio Shacks have ceased carrying ANY electronics parts. You're most likely to find solder, wire, switches, led's, and project boxes. The selection of transistors or IC's are poor to nonexistent. If you have a Fry's in your area, they have a much better selection, but their component prices are not much better then RS. Unless you need a part immediately, you'll be much better off getting it mail order.
Pricewatch is good for locating certain computer gear at its version of the best price. Froogle is sort of the same thing, but without the seedy side filtered out.
Smaller and niche suppliers
All Electronics (http://www.allelectronics.com) Corp. needs to even out their stuff a bit. Either specialize in a few types of parts or be more even across the board. Spark Fun Electronics appears to be trying to do it right. It is still weird that I can't just order a bunch of 0603 resistors from them. Seems like a no-brainer.
American Science and Surplus (http://www.sciplus.com/) has a little bit of everything. Rubber spiders, speakers, prisms, lab equipment, electromechanical timers, Slinkies, motors, switches, fake vomit, glow-in-the-dark pencils, radio-controlled toy rats... Good selection of fans and motors, and an oddball attitude to boot. If you're near Chicago, their retail store is even weirder.
American Science & Surplus seems to have good prices on breadboards.
Futurlec.com (http://www.futurlec.com) I've been very happy with Futurlec. Their prices are outstanding, especially on value packs. Their customer service isn't stellar, but in the end they've always resolved any problems that I've had. They ship from Australia/Thailand, but their shipping prices are reasonable & the shipping is quick enough.
microcontrollershop.com (http://microcontrollershop.com) - Large selection of development boards, programmers, debuggers for microcontroller projects. All major architectures ARM, 8051, PIC, Atmel AVR, TI MSP430, Freescale HC08, HC12, etc.
MPJA.com (http://www.mpja.com) - prototyping tools, components. Not a huge selection, but prices are low. If you order something that comes with an instruction sheet that was translated into English, the directions may be hard to decipher due to poor translation, possibly from Chinese. They ship from Florida.
For companies that supply a PCB customized to your design, see PCB Manufacturers.
I want to see some competition in the micro dev/app board market. I just paid approximately 34.95 + its share of the shipping for a 32 bit ARM microcontroller on a PCB and with a USB device port on one end and a series of header sockets on the other. If that is considered cheap, then this is never going to take off.
I realize that other authors will have different opinions than I, and that this entry is probably not going to remain as it is for long. Come on, everybody. These comments do not reflect the opinions of Open Circuits. They are only my own. Add yours.
I personally stay away from app boards unless I absolutely need to use them because of the price. Also the components tend to not be in sockets, so if you blow a pin or two on that $100 app board, you need to replace the entire board as opposed to a $5 microcontroller. Unfortunatly, many of the better parts are only available in SMT packages. Mzoran 15:30, 16 December 2007 (PST)
I've had great experiences with Mouser and Jameco for smallish orders (<$200). I've also had several good experiences with SparkFun. I now avoid Fry's. In addition to their horrible return policies, their stock is very random and prices aren't very good.
My personal experiance with Surplus Sales was very good. I would highly recommend them for anyone that needs a blower motor, hydraulic pump, etc. Good prices, good service.
Please note that IguanaLabs will be closing its doors for good on August 11th, 2007.
See also the list at http://techref.massmind.org/techref/supplies.htm .
Don't forget to check ebay if you're looking for fairly generic items. There are a number of suppliers that ship cheap components from China, plus a few who ship from within the US. I've gotten great prices on character LCD displays, pin headers, SMD LEDs, and PIC microcontrollers, among others.
ledshoppe has good prices on LEDs (all pin-through-hole). They don't have any other components, but they do have dirt cheap bluetooth dongles and SD card readers that may be of interest. Shipped from China, shipping is free. Usually arrives in the US in about a week, never had a problem with them.
Should comments be moved to discussion and a consensus formed around factual information regarding suppliers?