These are some of the vendors that provide products that enable end-users to update their own records in a directory server (most, if not all, of the products below are primarily AD focused though). This could include the ability to do password resets without calls to the help desk, but I was looking at their capability for managing opt-in/opt-out of distribution lists.
(Note: I haven't used any of these products, although several do offer live demos from their web sites)
Their Smart DL product allows end-users to create dynamic distribution lists based on AD attributes. I don't know whether they also provide an opt-in/opt-out capability though.
There are several different versions of their rDirectory product. However, according to their comparison chart, both the Professional and Enterprise editions offer a 'Group Self-Subscription' feature. The Enterprise edition looks to be a full-fledged IdM solution, with User Provisioning capabilites,
Their AD Self-Service Plus product looks to primarily be aimed at allowing end-users to perform password resets without calling in to a help desk, but according to the product page, one of the listed features is 'Update Personal AD Info'. I'm not sure if this could be extended to provide some sort of group/mailing list subscription capability though.
Like the Imanami product, the Group Management Portal allows end-users to create and manage their own distribution lists in AD/Exchange. Although from what I could tell from the live demo site, it seems to be only managed groups (meaning, members are manually added vs. dynamically updated based on user attributes)
And I would remiss if I didn't mention Microsoft's new ILM"2" product (which is only a release candidate now, but should available soon). This latest version of their identity management offering does have some pretty nice group management capabilities, along with the ability to delegate dynamic list creation to end-users. Of course, the primary focus of ILM"2" is user provisioning and the synchronization of identity data across many different target systems. But the rich end-user self-service interface is a nice differentiator compared to many other full-service IdM stacks out there today.