@bitcoinbot was displaying current market trades until September. I don't know how the information was being gathered, but I had only found them after they had stopped.

What sort of tweet volume are you targeting?

You could tweet every trade, but I do not think that would be an interesting twitter feed.

There is also a group blog setup at http://bitcoinmedia.posterous.com/ and I can add you as a contributor which means you can email the blog. This then gets blasted out to all the social media sites connected to it such as the facebook page and twitter. For instance I might subscribe to a newsletter and set the email address as the blog address and it autoposts the newsletter when it gets updated!