ClickZ: Choosing an Email Newsletter Broadcast Service

A list of questions you need to go through to prepare your purchasing process: build or buy, tracking and reporting, registration & subscription management, editorial interface.

For a much more in-depth look there's MarketingSherpa's brand new report (451 pages!): Buyers' Guide to Email Broadcast Services for Marketers & Publishers: How to Pick a List Host (this link includes an affiliate tag, thanks for supporting MarketingFix.)