Marco Buttarini

wg-twitter-widget is THE widget to show twitter status in wordpress sidebar. 
Developed starting from the existing widget of Sarah Isaacson, * using the example widget of Justin Tadlock

WG Twitter Widget

Twitter Widget Highly configurable, with image and last twit of users

Aaron D. Campbell

A widget that properly handles twitter feeds, including parsing @username, #hashtag, and URLs into links. It supports displaying profiles images, and even lets you control whether to display the time and date of a tweet or how log ago it happened (about 5 hours ago, etc).
<a href="http://aarondcampbell.com/wordpress-plugin/twitter-widget-pro/" rel="nofollow ugc">Twitter Widget Pro</a>

Twitter Widget Pro

A widget that properly handles twitter feeds, including parsing @username, #hashtags, and URLs into links.

WG Twitter Widget vs Twitter Widget Pro