plug ins

is there somewhere a complete list of plug ins?

I am looking in particular for the following:
* that people can only read part of the post, unless they register
* that I can find out automatically where they are from
* that I can put in new posts via email
* that people after registering can make comments
* that they can repost to Facebook, twitter etc.

Any help would be very much appreciated. Is there are wordpress for dummies? 🙂