This list will be a continuous work in progress. If there is something you feel should be on here that isn't, please feel free to get in touch.

Arcade Part Suppliers (Europe)

• Arcadeshop.de - Joysticks, PSU's, Coin mechs and lots more.
• Suzo / Happ
• Brent Electronics
• Swallow Amusment Machines

Arcade Part Suppliers (US)

• Arcadecomponents.com - Parts for Old Arcade Games
• Lizard Lick Amusements - Various Parts including sticks and Cap Kits (thanks ColinD)
• Mikes Arcade - Specialises in Nintendo and Midway Parts & Machines
• Quarter Arcade - NOS Artwork, Parts and machines.
• Two Bits - Pacman & Pinball Parts

Artwork, Manuals & Schematics

• ARCade ARChive - A wealth of technical docs, artwork and magazines (thanks guddler)
• This Old Game - CPO, Bezel, Side and Coin Mech Repro Artwork
• Crazy Kong - Artwork, Manuals, Pin Outs and a whole lot more!

Reference

• CPS2 Shock - Capcom CPS / CPS2 Information

Tutorials

• Cooper Tools - Basics of Soldering (pdf) - (Thanks robin_l)

Repairs

• Braze Arcade PCB Repair Tips
• Channelmaniac's Arcadecomponents' Old School Repair Logs