It is no secret that I use up more solder than log books. But it has been getting harder and harder to buy parts. Sure, everyone knows about Mouser and Digikey, but they are expensive and don't have a lot of RF parts. Here's some places I like:
Dan's Small Parts - Incredible! This is the place for RF projects.
Alltronics - When I go to San Jose, I like to try to schedule a free day so I can go the "Geek Shops" (as my XYL calls them). This is a good one, and they have a good catalog too, so even if you can't get there in person, you can still order.
All Electronics - Not a bad catalog.
Electronic GoldMine - Another good catalog full of odd parts. We even got a hygristor (humidity-sensitive resistor) for my son-in-law's school project here.
EPO - Everyone's favorite Clear Lake area store is on the Web. If you don't live in the area, you can't get the full flavor of the place on the web (yet).
Circuit Specialists - This place is a good source for PCB etching stuff.
Silicon Valley Surplus Sources - This guy knows where all the geek shops are in the valley. I actually went to about 80% of these in one day! That's harder than work!
RF Parts - What else? RF Parts.
KitParts - Tom N3LLL's site has lots of hard to find parts.
Do you know a good place to buy parts in the US? e-mail me at firstname.lastname@example.org