Canadian Error Coins
Patrick Glassford's awsome site has been the inspiration to mine

Mike Wallace's error coins
great pictures and explanations of various errors

Error World
best online club for error coin enthusiasts, and it's free

World Errors
lots of information about world mint errors, and some spectacular photos

Asfanet
Israel Collector's Net (in Hebrew)

William M. Rosenblum
best coin dealer around for Israel/Palestine/Ancients and a few other topics

Error Trends Coin Magazine
site maintained by Arnie Margolis, error dealer and author of "The Error Coin Encyclopedia"

Charles Calkins' online coin collection
Beautiful collection with some of the best scans seen on the net. Also has a great section on how to scan coins

Fred Weinberg
notable error coin dealer

Mike Byers
error dealer dealing exclusively with items in the $1000-$100,000 range.  Wow.

How to convert Jewish dates found on Israel coins to Gregorian calendar
on this site.