Aelora

rTwit adds a short code that allows you to embed any Twitter feed into posts and pages on your WordPress site.
This plugin came about from my need to embed tweet from software authors on a page describing the software.
Requests are cached for 30 minutes, by default, so that subsequent page views can load from cache rather than having to reload and reparse the Twitter feed. Links are set to open in a new window, although that is optional.

rTwit

Quickly embed any twitter feed into a post or page.

Adam Nowak

This plugin adds a customizable security question to the sign up form. You can choose your own question and answers. Multiple answers are possible, you can have a question like: Do you like cats or dogs and have both as acceptable answers. The goal is to fool the spam bots. Change questions as often as you need, it’s easy. The plugin can’t stop spam altogether, but every little bit helps.

Buddypress Humanity

This plugin adds a security question to the Buddypress registration page.

rTwit vs Buddypress Humanity