Here are a few links to help you on your path to arcade nirvana:
KLOV - The Killer List of Videogames - A great resource for arcade enthusiasts. I am a moderator on the message board, which has many seasoned pros at the game of arcade owning and restoration.
VAPS - The Video Arcade Preservation Society - A listing of arcade collectors and the contents of their collection. My listing is here.
HardMVS - A Neo*Geo site that has quite a bit of info.
Internet Pinball Database - A good pinball resource. I don't like the way it is structured, but it gets the job done.
Randy Fromm - Randy offers great technical advice in his 'technical department' as well as running arcade repair seminars.
The Real Bob Roberts - The first place to go with parts questions! Bob Robert is an expert at repairs, and he's willing to help you out if you email him.
US Amusement Auctions - A national auction company that deals in arcades.
Super Auctions - Another national auction company that deals specifically in arcades.
United Amusement - An auction company local to the Kansas City area.
Hyperspace Arcade - A repair service run by KLOV board member TexasHotshot.
RK's Arcade - has a great flowchart to help with your Q*Bert sound troubles. Helped me isolate the source of my sound woes.
Basement Arcade - Great site all around with lots of resources, but the part I found most interesting is the auction listings from the New Jersey area (the reason I post KC auctions on my site ;).
Arcade-Classics.com - Evil Exidy has a great collection.
Brian's Arcade - prOk's site. He's got some really helpful restoration stuff on his site, not to mention a sweet collection.