Reminder Forwarding is the most useful Outlook add-in that I have used. It is the only tool to send outlook reminders to your cell phone or email address when you miss them.
The link for this tool is http://www.reminderforwarding.com .
There are other tools that send every reminder to your email or phone, but I find that very annoying. I don't want to get messages on my phone when I can see the reminder on my screen. I only want to be alerted when I am not at my computer. This does it right.
This is the best outlook add-in that I have found and it has my vote!