Constant Contact would work perfect for you I would think. We have used it in house here and a few of our agents also have their own accounts. You pay monthly based on how many people are in your mailing list. The list of templates is vast and very customizable. You can use it to send out newsletters, cards, just listed/just sold, or whatever else you can think of. All Constant Contact emails also use a safe un-subscribe for people who feel they are being spammed.
One nice thing about the service is that is also scrubs your list for you. Each time you send out a mailing, it records which addresses no longer exists. You can create groups of email addresses for different uses and if you email out to more than one group, the system does not duplicate the email for people who belonged to both groups.
All in all, it was a nice find when I first ran into it a year or so ago. They also offer a free trial so you can check it out before you pay. Good luck!
I currently use Top Producer with Outlook Connect and it's good. Within SoCal MLS / Tempo under "my tools" you should try MLS-Office. It's inclulded in your dues and I believe you can upload your contacts from an export of ACT.