Who has the best email list for contacting e-marketers in the USA? I
am interested in knowing if any lists/companies are better than others
for different types of markets.

A good place to start is with a list broker.  Most traditional list
brokers now also offer email lists.  You won't pay any extra for using
a list broker -- they receive a commission straight from the list
owner -- and you'll get their expertise of the list market.

Google's category listing is at:
http://directory.google.com/Top/Business/Marketing/Direct_Marketing/Mailing_Lists/?tc=1

Someone I've used (and like) is Mark Aaron at aaronlist@comcast.net or
800-470-LIST.