Here's actually what I think are the 14 most important, either because design care is needed, or because they're common, or because they are early-on in user conversion...
notifications
(in general)
new reply to your support ticket
someone added you as a friend
new comment posted
your content was liked
new topic posted
new private topic opened with you
topic replied to
it's a friends birthday
notification digests
newsletter with automatic what's new content
recommend website
lost password reset confirmation
join confirmation
notifications
(in general)
new reply to your support ticket
someone added you as a friend
new comment posted
your content was liked
new topic posted
new private topic opened with you
topic replied to
it's a friends birthday
notification digests
newsletter with automatic what's new content
recommend website
lost password reset confirmation
join confirmation