Office Live Workspace (Beta)
It's not often I wax lyrical about a Microsoft product, but this just works well.
It's not new, but it's useful, especially as I had my lappy nicked recently & lost scads o work as the pendrive it was all backed up on was in the lappy bag, along with my graphics tablet & phone.
Still, I remembered I had signed up for this a while back & I've now started to use it. I can now sore my Word 2007 docs either locally, or more importantly online with automatic saves so my work's never lost. Like Google Docs I can share & collaborate with other users, but I can also view Powerpoint & Excel docs without having Office on the computer I'm using.
Like I said, it's nothing new, but it's new to me & being able to open & save directly from Word is just a lifesaver. Dunno why I didn't use it (or Google docs) before. Could have saved myself hours of work.