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

Simivar

Adds a sidebar widget to display Twitter updates (using the Javascript). You can set number of messages, color and other features.
You can change colors of shell background and shell text; tweet background, tweet text and tweet link. You can set on/off a features like scrollbar, show hashtags, poll for new results, show timestamps/avatars and the behavior.

Advanced Twitter Profile Widget

Adds a sidebar widget to display Twitter updates (using the Javascript). You can set number of messages, color and other features.

WG Twitter Widget vs Advanced Twitter Profile Widget