Email List Management

Depends on the size of your organization and list size.

Small businesses looking for free stuff:
You can use free tools like Bravenet.com's email services. They are ad based though.

SME: Low budget: No fancy targeting needs.
Aweber, Bigresponse are pretty good.

SME: Large lists:
ExactTarget, BlueHornet, Silverpop, ConnectPop, eCircle are all great ESPs that allows you to target emails based on whatever criteria you want. Send x email on that day at this time based on age, geo, product bought plus you can also send multivariable testing emails.

Hope that sheds some light on your question. If not let me know so I can clearify some more. :)

Cheers
Chris
www.reallyhotideas.com