Arcade Parts

The Real Bob Roberts - Arcade Game Parts Galore
This Old Game - awesome arcade art and parts!
Phoenix Arcade - more awesome arcade art.
Wizzes Workshop - some fun stuff there.
Lizard Lick Amusements - sells new and used arcade parts.
ArcadeComponents.com - your source for old and rare components for arcade games.
arcadecup.com / monitorboss.com - guess what they specialize in? A hint... monitors!
Cinelabs.com - they do monitors, too!
Arcade Shop Amusements - Your source for classic arcade games and parts
Arcade Games.com - Arcade Games, Arcade & Game Room Equipment
Quarter Arcade.com
Mike's Arcade.com
VideoGameParts.com
Mike Doyle's Famous 96 in 1 Pac-Man Multi Kit
Happ Controls - Distributor and Manufacturer of Parts for the Gaming, Amusement, Industrial, Vending and Interactive Industries

Arcade Art

Local Arcade.com
Star Trek scanned artwork at Zinfer.com

Components

Digikey.com
Mouser.com
Jameco.com
Farnell.com
Allied Electronics.com
All Electronics.com
Futurlec.com
Arcade Chips
4 Star Electronics - Obsolete Semiconductor
BG Micro
NTE Electronics
Newark
State Electronics - Potentiometers
First Choice Components
ACP Components
CTS Corporation

Community

The Killer List of Videogames
The Killer List of Videogames Message Boards
The Great Game Database
RGVAC - rec.games.video.arcade.collecting Newsgroup
CoinOpSpace.com - Classic Arcade, Pinball and Console Collecting Gaming Community