Currently the main place to check out EM's is on the Pinball database.
Pinside are now taking your ratings so a Top 100 EM list can be generated - and require 10 votes for each machine for the list to be displayed to the public. So please enter a few ratings for machines that love or hate so then we can have another resource to base any purchases off.
http://pinside.com/pinball/top-100/em