What site access control plugin do you use?

I've been doing some searching around the forums and on wordpress.org to find a good membership control plugin. I'm wondering which one people from the community use and would recommend.

I'm using buddypress/bbpress. I know normal CMS systems use some form of membership control via groups/roles. Wordpress by default doesn't have this , so just looking to see which one is the most popular and doesn't hit the site with slowdowns.

Thanks for the help!