We have a number of mailing lists for various topics, and sometimes people aren't sure which ones they've subscribed to. I would like to send a newsletter to our main mailing list (group) with an option to go to a form (profile) that lists ALL the mailing lists/groups the person is included in. Ideally the form would allow them to unsubscribe from any they don't want to be in as well.
Please help!
Have a look at the CiviCRM Tokens wiki page: http://wiki.civicrm.org/confluence/display/CRMDOC/Tokens
I think the one you'll be most interested in is {action.subscribeUrl} which provides a link to view and subscribe to any public mailing lists.
You could also build a profile with the groups field in it and sent it out via a checksum token. This will link the details to their record and allow them to update. This is useful if you want them to be able to update other information at the same time.
Full details on the checksum token at the bottom of the wiki page.
Depends on how you want that a user sees this. If you mean by user someone who could login into CiviCRM and see his/her own contact summary then they could see which groups they are part of.
If you mean by user the recipient of a mass mailing you could use tokens as explaind by Heather O.
If you mean by user someone who could login into drupal/wordpress/joomla but doesn't have access to CiviCRM then you could use your CMS system to build a custom profile page. In Drupal you could use Drupal views for this task.
If your groups are Public then directing people to civicrm/mailing/subscribe?reset=1 should show them a form where people can sign up (or unsubscribe) to any of your (public) mailinglists
or perhaps civicrm/?page=CiviCRM&q=civicrm/mailing/subscribe&reset=1 for wordpress
