David Ferguson recently released AlfredTweet, a great Alfred extension for doing all kinds of things with Twitter. Check out his blog post on the subject. This extension had everything I needed except for Twitter list management. I have added the following commands to AlfredTweet:
tw lists - Show lists
tw add - Add user to list
tw remove - Remove user from list
You can grab my modified version of AlfredTweet from github, where I forked David's original repo. Simply replace script.php located at /extensions/scripts/AlfredTweet/. For ease of use, I have also exported the modified AlfredTweet Extension. You can download it below.
Update: Devid Ferguson pulled in the list related additions I made to his repo! You should use his repo now as he is making additional improvements. Check it out!