I've long been a fan of the WordTwit plugin from BraveNewCode and used it on both Voxeo's blogs as well as my own to auto-tweet out new blog posts. Given that I write 99% of my blog posts offline (using MarsEdit) and send them to the blog site for posting, the fact that I couldn't configure the resulting auto-tweet in WordTwit was never really a big deal to me. Some of my Voxeo colleagues who used the WordPress editor, though, really wanted to be able to modify the auto-tweet.
Primarily they wanted to add hashtags, although sometimes they wanted to change the tweet to be different from the title of the post.
The BraveNewCode folks came out with WordTwit Pro back in June and with my chaotic summer I'd never really taken a look at it... but now that I have I admit to being quite impressed! This video gives a great tour:
I admit that what I personally find most interesting is the ability to automatically schedule multiple tweets. I know from my own reading of my Twitter stream that there is no way I can even remotely keep up with the stream... and so I only see things that happen to come by at any given time. I've often thought about auto-tweeting a blog post... and then tweeting it again maybe 8 or 12 hours later when a different group of people may be monitoring Twitter. This plugin now helps automate that.
I haven't installed it yet on my own site... but I'm definitely thinking of doing so...