List of Office Outlook 2010 add-ins
You are probably not going to find a comprehensive list, but you can find links to ones that people compile and feel are the best:
http://email.about.com/od/outlookaddons/tp/most_popular_outlook_add_ons.htm
http://www.techsupportalert.com/Best-free-outlook-add-in.htm
I Googled "outlook 2010 add-ins" and "outlook 2010 add-ins best" (both minus the quotes).
Are you looking for one in particular?