Guido Scialfa

Disable the user registration through the wp-login.php page, also redirect all actions like lostpassword, resetpass etc…

Disable Register

Disable registration through the wp-login page.

shawfactor

This plugin allows you to turn of or shutdown registration via Buddypress, without effecting other functionality.
I built this as I don’t like the way Buddypress does registrations but liked most of the rest, but you could use it if your site was full or invitation only for instance.

LH Disable BP Registration

Shuts down registration via the usual Buddypress method, all other functionality is not effected.

Disable Register vs LH Disable BP Registration