I collected a few more CMS vendors who are on Twitter. I was having some technical difficulties with the table I started here, so I decided to put it in a spreadsheet, which you can download by clicking here. My thanks to folks who commented on the initial entry and added me on Twitter. If you know of more, feel free to comment here. Better yet, updated the spreadsheet and send it to me via email and I will keep it up to date and post it regularly.
UPDATE (4/14): Already added a few more, so download it again if you need to.
UPDATE (10/12): As Oliver notes below, we have moved the list of CMS vendors to Tweeple.org. It’s a great way to look at the whole list we have developed, and choose to follow all or some of them with a single click. You can also suggest additional companies there.