TwitStamp
Highly customisable with different size and style. The most important is that it’s free and worked.
Widge Box
Nice design and customisable background colour, auto-scrolling twittes. HTML code available in javascript, flash or MySpace specifically. Get the Pro version to remove the ad button.
http://widgetserver.com/syndication/flash/wrapper/InsertWidget.swf
Twitt-Twoo
Great twitter widgets for your WordPress site. This is more programming involved to install, but highly customisable for your needs.