This isn't a definitive Pinball Links page - rather a selection of quality sites I think are worth looking at.

Stern Pinball - the only manufacturer of pintables at present
Pinball Owners Association - you should join, you really should!
The IPD - Home of the Internet Pinball Database
Tilt It - Really good Italian site (with English text too)
Terry Cummings - Lots of pinball history
Pinball Heaven - UK supplier of machines and spares
The Getaway - Read my review then check out this great appreciation site for the game!
PinLinks - A huge number of links, search for specific machines on the web.
Pinheadz - Quality site, specialising in restoration. Lots of links too!
Pinball Nostalgia - Lots & lots of great pictures!
Marvins Technical Page - Plain English guides to repairs, both electronic and Electro-Mechanical. Excellent!
House Of Pinball - English & Dutch site, includes the Pinball Top 100!
Instruction Cards - 300 plus scorecards, invaluable if yours is lost!
Pinball News - Find out the latest news and views
Manual Archive - Manuals available on CD Rom and much more
Pinball Manual Site - About a million manuals to download for free!
Shiva Site Superb site, news, manuals, backglasses, flyers - everything you could want for pinball
Flyer Archive Hundereds of flyers online - amazing!
Bally CPU Review Replacement CPU boards for your old Bally/Stern game reviewed
Pinball Sounds Fantastic electronic game sound archive
Score Cards Lots of instruction and pricing cards to print
Defender Great site from Dave Langley, about restoring his Defender
More Defender! Jim Askey's site, tech stuff, owners list and more
Rule Sheets Find out how to really play your game!