Time for a new weapon in war that is e-mail marketing. Trying to land business using Microsoft ( MSFT) Outlook, Google ( GOOG) Gmail, Yahoo! ( YHOO) Mail, Apple ( AAPL) Entourage or any of the dozens of e-mail tools on the market is a serious pain. On the face of it, e-mail marketing is a lovely thing for small businesses. With a fat e-mail list, one should be able to print money. But converting those potential dollars into cash is an exercise in insanity. Sometimes messages go through, sometimes they don't. Sometimes customers respond, sometimes they don't. Sometimes subject lines resonate with client, sometimes they don't. And nobody knows why. Many small shops rely on e-mail marketing firms. We have used Constant Contact (stable, but inflexible) and FeedBlitz (powerful, but difficult to use). This week, we move to our next contestant: Atlanta-based MailChimp. The company offers basic accounts for free, which limit the number of subscribers and e-mails that can be sent. But for $250 a month, users can have 50,000 subscribers and send unlimited mailings. We have been testing the system internally for about a month. And it seems ready for primetime. What you get: a powerful e-mail tool at a reasonable cost. It's clear that a lot of time and money went into making the site easy to use. Users navigate MailChimp through simple menus with names such as Dashboard, Campaign, Lists, Reports and Autoresponders. This is a vast improvement over the sequential screen layout of Constant Contact, which feels like a never-ending Mensa exam.