User Permissions Plugin

Can someone recommend a good plugin to assign permission to wordpress users to only be able to use other specific plugins?

ie: “Moderator” user-group permission group can only see “Polls” plugin and have the ability to post and edit options when he/she signs in.

I have a series of plugins such as “Polls” and “Espresso Event Management” that I only want certain user groups to be able to use and see. They may or may not have access to standard features such as Page, Posts, Portfolio, etc.

Also, what are the best ways to design a custom user registration page? WP-MU any good??