1. Make a Twitter List. Here's one I created for Boston Media Makers attendees.
2. Go to Twitter Lists 2 RSS.
Enter the URL of your Twitter list.
Click Get an RSS Feed.
Then you get an RSS feed:
3. Follow the steps at Wordpress.com on how to make an RSS Widget.
In Wordpress, got to Appearance, Widgets, and drag the RSS Widget to your sidebar.
Add the Twitter RSS feed you just created and save it.
The feed is now displayed on your Wordpress.com sidebar.
If there's a problem displaying tweets, it's probably a limit rate between 'Twitter Lists 2 RSS' and twitter.
See it implemented at Boston Media Makers Wordpress.com blog.
It'll get better. ;-)
It got better.
Twiter unveils twitter list widget. Wordpress .com strips out the script code in the Text/HTML wdget though. Lame.