Part Sources: arcadedepot.com - They built the cocktail kit that my table was made from, probably the most helpful and flexible company on the web. twobits.com - I bought my glass and underlay from them. happcontrols.com - The source for almost any arcade part. ultimarc.com - Source for J-Stiks joysticks and I-PAC encoders. arcadeshop.com - Tons of arcade parts, I got my speaker/vent shields from them. wellsgardner.com - The most prominent of all arcade monitor manufacturer's. I got my U3100 from them. gamecabinetsinc.com - okay starter plans for a MAME cocktail table, but very good prices on arcade parts
MAME: mame.net - The official MAME site. Mame32 + - The best windows emulator I have found yet. MameGuy - Member of the Tombstone network - I got my ROMs burned from him.
Other MAME Cabinets: Johnny's Pacman-Mame - Johnny and I have been trading info back and forth as we both work on our tables. Check out his great website to see his progress. Blake's MAME Cabinet - Friend of mine working on an upright MAME cabinet, although not updated in a while, his info conviced me that something on this scale could be done.
Other Info: Build Your Own Arcade Controls - A HUGE repository of information covering everything from cabinet construction, monitors, arcade controls and more. They also have a large index of example projects.