The ultimate plugin and service to stop and kill splogs in WordPress Multisite and BuddyPress, from WPMU DEV.
Anti-splog tank of doom!
Limiting the number of signups per IP
Changing the signup page location every 24 hours
Random user defined questions
Recent splogs queue, notice all the instant actions!
Suspected Blogs queue
Instant spamming of an entire IP address
Instant post previews
Instant full blog previews
Anti-splog process Flowchart
Site/Splog creation statistics