DocVerse is a pretty cool product I came across a couple weeks ago. It was written up in GigaOm here, so obviously I don't read everything out there :)
It allows to you collaborate online with MS Office software. The initial focus is on PowerPoint which is an obvious starting point and something that was needed. Especially as travel budgets get cut, online collaboration will become more commonplace and PowerPoint is a good market to target. It's in private beta, but you can download their plug-in here.