I get pretty put out when someone gives me a gem every 50 tweets but the rest are pitches about their software, ads for seminars and webinars or telling me what they had for breakfast.
This list has the people I have seen being the most consistent dedicated email marketing tweeters.
It won't be perfect but it is the best I have found, so far:
http://twitter.com/getintheinbox/bestofemailmarketing
