Issue Reminders JIRA plugin allows you to create multiple reminders to issues in addition to global due date reminders. You can send reminders to users, groups, project roles and an email address at the same time. Reminder can be periodic or can be relative to any date field. Emails are not just a link to JIRA issue, they also contains rich text description of the issue so that the recipient does not need to access JIRA to see issue. This is especially important for external customers who does not have access to JIRA. You can create your own template too.
You can also obtain a list of all issues with a reminder using 6 different JQL functions or you can see all of you reminders in My Reminders page.
Plugin also provides a REST API so that you can integrate your own applications with the plugin.