BlockParty - Real-time voice chat rooms from the creators of turntable.fm
Twitter Block Chain - Chrome extension to block all followers/following on a page
Secateur - Use Secateur if you want to temporarily or permanently block or mute (or both block and mute) a Twitter account and all its followers.
Mirror Block - Mirror Block is a browser extension that allows you to block users on Twitter.
Boyfairy - Your opportunity to educate right before you block someone.
Red Block - Red Block is a browser extension that lows you to block users from your Twitter account.