FindChips.com If you know your part number, go here and search more than a dozen popular distributors at once! It's on my toolbar right next to Digikey and Google

Octopart.com A new type of engine where you actually type in the description. Has photos, but still in development!

China IC Mart If you are buying in sufficient quantity, this search engine allows you to find sellers with the ICs you want. Ed. note: These 'IC search' systems tend to be grade-A 100% nonsense

This has been moved to Boutiques

These places are massive, and stock pretty much everything!

Digikey The best in the business: gigantic collection of in-stock parts, reasonably low costs, amazing searchable website, will sell small quantities of most stuff, doesn't rip you off for shipping and (most importantly) ships your order within the hour. Yes, hour. Next day really means next day. Get their catalog & cuddle it before you go to bed…they're more dependable than your boyfriend ever will be. Currently Altium Designer (EDA suite) now has a direct database link from their parts library to Digikey's inventory. Should be the first or second place to start any project, don't spec anything in unless Digikey or Mouser has it (if at all possible).

Mouser Second only to DigiKey, Mouser is a hot-shot distributor with often-cheaper prices and if you place a large order they'll often upgrade your shipping from UPS ground to 2nd day! Based in Mansfield Texas, and if you are shipping in Texas all shipping (ground) is next day. Should be the first or second place to start any project, don't spec anything in unless Digikey or Mouser has it (if at all possible).

Allied A so-so company, but tend to have a lot more things like switches, pots, etc. than the above. More of a traditional distributor, less in stock but can stock items if you order large quantities.

Newark/InOne/MCM Nobody likes Newark, so use them as a last resort. They'll charge you $25 to ship a small cardboard box by UPS ground. Grrr. More of a traditional distributor, less in stock but can stock items if you order large quantities.

(Oct.2010) – I've found Newark to be pretty good. Useful Web interface (sortable results in all categories, including price), and prices frequently better than Mouser or DigiKey, particularly for smaller quantities. They will now ship via USPS, FedEx, or UPS ground, starting at about $5, depending on weight. Seem to be pretty good about in-stock items too.

http://australia.rs-online.com/web/ Their range is amazing but so are their prices. When I first saw them I thought I was dealing with a different currency.

Arrow Electronics Another traditional distributor. Use only if you can't find what you need from Digikey or Mouser.

Future Electronics Another traditional distributor. Use only if you can't find what you need from Digikey or Mouser.

Avnet Another traditional distributor. Use only if you can't find what you need from Digikey or Mouser.

All American Another traditional distributor. Use only if you can't find what you need from Digikey or Mouser.

NuHorizons Another traditional distributor. Use only if you can't find what you need from Digikey or Mouser.

TTI Another traditional distributor. Use only if you can't find what you need from Digikey or Mouser. Currently owns Mouser, but does not have cross inventory control or supply.

Jameco Electronics Yet another. Does seem to specialize in hobbyists. Has its own line of branded commodity parts. Many components only sold in large quantities (e.g.: resistors only available in packages of 100 but they are $1.50-$2 for the package).

Distrelec Large European distributor. Cheap components (e.g. resistors, general purpose transistors) only available in packages of 100.

Techni-tool Carries essential lab equipment such as o-scopes, irons, solder, test equipment, microscopes, PCB supplies, etc..