BuddyPress First Letter Avatar is a simple plugin that gives a colour coded avatar based on a letter from the username of the user, for users that have not set an avatar image. It’s an alternative to assigning a Gravatar or similar. It also performs the same task for Groups.
Buddy Registration Widget is an unusual plugin in that it is very mission specific, it will add a widget that displays the BuddyPress registration page, it disables the BuddyPress member profile cover image site wide and it won’t allow new members to access the site until they have set uploaded a profile avatar image. There are no settings to change, once uploaded these options are set and that’s it. So if your site has these specific requirements then this plugin is for you, but if you want registration in a sidebar widget but also want profile cover images then this plugin is not an option!