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One of the great frustrations of electrical engineering is part obsolescence, price and scarcity. In accordance with engineering law, half of what's ordered is never used and the other half's not enough. The most popular style of EE hacking that I've seen is a pack-rat approach where everyone amasses 'a few of everything', perferably for free or scavenged. Granted, IC's are relatively cheap for their functionality, ranging from $.60 for a 555 to $15 for a high-speed digital signal processor, but they add up fast. (Especially since you'll need at least 2 of everything in case you short one out.) Passives add a few dollars too, and connectors can end up biting you if they're not spec'd well. And all that after dropping a few hundred dollars on a scope, meter, power supply, function generator and EEPROM programmer, not to mention the wire, boards, hand tools, etc.
In these days of low-cost, all-in-one Taiwanese epoxy-boards, just finding someone who will sell you "3 of those" can be a headache. Many hobbyists, myself included, are leaning towards "if you cant get it from Digikey, then I'm not going to design with it." Regardless, there are some tricks that can make your small-scale project easier to manage…
It's hard to go wrong with free. Parts manufacturers are often more than happy to ship you, for no cost, a few samples of their merchandise. They often ship within the week, sometimes the next day, and with free 2-3day FedEx/UPS.
These are only the half-dozen companies I've actually ordered from, if you know others, feel free to edit the wiki (or email me)!
The de-facto standard for annoying microcontroller design. Regardless, it's up there with the 8051 and AVR in popularity. It seems like you can get their more popular <$5 microcontrollers sampled. Also, of course, are their little flash memory chips, mid-freq RF chips and 'analog glue.' According to their FAQ, you can get 3 of 5 different parts, twice a month, shipped via 3-day.