Here you'll find my most up-to-date list of resources for parts. There's also a description of each of the vendors with stuff to look for and avoid from each. Lastly, there will be a breakdown of how I usually order parts for a build.

Vendors 

Tayda Electronics

This is a great resource for passive components (resistors, capacitors, potentiometers, etc.). They are based out of Colorado but also have a location in China that handles a lot of their orders. I've never had to wait more than a week for a shipment to arrive and I live on the east coast.

They have the lowest prices of anyone I've seen for components in general too. Most of their potentiometers come with a plastic covering on the back (a.k.a pot condom) that prevents your PCB from grounding out on them. In addition, you can buy resistors in packs of 10 for as low as $0.01/each. They have a good selection of capacitors (film, box, electrolytic, monolithic ceramic, and ceramic disc). There's also a decent selection of axial caps that carry some nice mojo to them. I also like the selection of opamps they carry and the TC1044SCPA charge pump all of which are incredibly well priced.

This is a great place if you really want to try something out without putting a bunch of money into it. There's a minimum order of $5 but that usually gets you at least a pedal's worth of parts.  Their customer service is quite good as they usually respond within a day. If they get something mixed up in your order they will usually give you a nice store credit or refund (store credit is usually higher).

On the downside, some of their transistors and diodes, mostly JFETs like the J201 and 2N5457 as well as germanium diodes, have been proven to be counterfeits. I highly doubt that was intentional on their end. The Chinese market, where they get their parts from, is flooded with fakes so it can be quite hard to discern the real ones sometimes. Plus those components can still work in your build, you just have to bias the JFETs properly and try different diode combinations.

Their enclosures can sometimes be on the cheap side. However, they are starting up a new finishing department which could be really cool. They do already provide enclosures in certain colors and buffed.

What to buy:

• Resistors
• Capacitors
• Diodes
• Transistors
• Opamps
• Potentiometers
• Power Jacks
• Wire (stranded and solid core) 
• LEDs (and bezels)
• Knobs
• Sockets (to swap out ICs, transistors, diodes, etc)

What to watch out for:

• JFETs
• Germanium components
• Bare enclosures
• Input Jacks

BLMS

Lawrence Scaduto runs the best shop on the market for enclosures, switches, input jacks and cool knobs. He also has one of the most hilarious names in the industry: Bitches Love My Switches. Aside from that, Lawrence also carries some helpful extras like daisy chains, patch cables, 3PDT daughterboards, etc.

To top it all off, if you live in the US then he does flat rate shipping on all his items. I've purchased 50 3PDT switches, 5 true bypass looper enclosures, 120 input jacks, and shipping only ever costs $5.99. He usually ships same day and I've never been waiting more than 4 days for anything I've ordered.

Get on his mailing list as he does updates on new products and sends out sales on items he's clearing out.

What to buy:

• Anything and everything.

What to watch out for:

• Nothing. He lets you know what the quality of each item is in its description.

Small Bear Electronics

Small Bear is one of the most recommended sites for builders. They have everything you need and then some. If there's an obscure part you need for your germanium fuzz then they have it. This is where I go for more obscure or out of production ICs and transistors. You can purchased matched JFETs and germanium transistors for fuzz builds (they even sort them by what type of fuzz they'll work well in).

The one downside is that they are a bit pricier than other retailers. But considering you won't have to buy 15 germanium transistors to find two that match for your fuzz build it's worth the extra cost.

What to buy:

• Germanium anything
• Specialty ICs
• Finished enclosures

What to watch out for:

• Nothing in particular. You'll probably want to buy passive electronics elsewhere because of cost. But everything Small Bear sells is good quality.

Mammoth Electronics

Mammoth Electronics is another one of the more popular sites for DIYers. It's geared specifically towards guitar effects rather than sites like Tayda and is really easy to navigate. They have a wide selection of effects kits and partner with some really great PCB designers like Grind Customs FX. On top of that, there's a fantastic selection for enclosures. They have the typical variety which can all be custom drilled and painted for you (for a reasonable fee) and a huge selection of other sizes as well.

Their IC and transistor selection is top notch as well. There's no counterfeit parts to be found here and have a good selection of discontinued JFETs (J201 and 2N5457) required by a lot of amp-in-a-box builds. They also have one of the widest switch selections available. Their 3PDTs are differentiated by grades rather than the standard "Taiwan Blue" switches available at most other retailers.

Mammoth is a bit pricier than sites like Tayda but that's mostly due to being a US based business. While Tayda saves on overhead by employing some overseas workers, Mammoth is based out of Oklahoma and does all of it's own custom orders (mostly enclosures) in house for quality control. They also have to factor in things like parts testing to make sure they aren't sent a batch of fakes, which does add cost. So while your order may be a bit pricier from them, you know what you're getting is the best quality out there.

What to buy:

• Enclosures
• Transistors
• ICs
• DIY Kits
•  Switches

What to watch out for:

• Nothing. Although your passive electronics are usually not a quality concern so you can buy from places like Tayda for a much lower price (order double if you're concerned and it will probably still be cheaper).

Summary by Parts

Passive Electronics

Resistors - Tayda Electronics
Capacitors - Tayda Electronics
Potentiometers - Tayda Electronics
Sockets (for parts swapping) - Tayda Electronics

 Active Electronics

Transistors - Tayda Electronics & Mammoth Electronics
Opamps - Tayda Electronics & Mammoth Electronics
Specialty ICs - Small Bear Electronics

Hardware

Input Jacks - Bitches Love My Switches
Power Jacks - Tayda Electronics
Enclosures - Bitches Love My Switches & Mammoth Electronics
Footswitches - Bitches Love My Switches & Mammoth Electronics
Knobs - Bitches Love My Switches & Tayda Electronics
Toggle Switches - Tayda Electronics & Mammoth Electronics
Wire - Tayda Electronics

My Order Process

This is how I typically separate parts of my order for a build.
Tayda Electronics - Resistors, capacitors, potentiometers, ICs, general purpose transistors (not JFETs), wire, toggle switches, sockets, and knobs.
Bitches Love My Switches - 3PDT, enclosure (if I want a basic one), input/output jacks, thinline power jack (since I don't use batteries)
Mammoth - JFETs, specialty diodes, enclosure (if I want something very specific or pre-painted).


Now that you've got all your parts, it's on to the Build Procedure