You can now share lists of reminders from the iCloud web site (not individual reminders, however). To do this, hover your cursor over on a list in the left-hand column of the Reminders interface, then click in the little round sharing icon that displays at the right of the list's name. Enter an e-mail address for the person you want to share the list with, then click Done. You can add several people if you wish. Any of the users of these shared lists can add or delete reminders, or mark them as completed.
You can also do this from the Reminders app on OS X, but not yet from the iOS Reminders app.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20121022000618273