CloudOn, which has allowed iPad users to connect to its cloud-based versions of Microsoft Office apps for some time now, has released an Android tablet version of the app. As with the iOS version, you can sync it up with either Box.net or Dropbox, and with the release of the Android app CloudOn is naturally adding support for Google Drive to the mix. Otherwise, it's essentially the same interface and feature set as you'll get on an iPad, which is to say a full version of Office hosted in the cloud along with a side of Adobe Reader for other files.
Office's desktop interface is obviously far from tablet-optimized, but the tradeoff in this free app is that you shouldn't have to worry about losing formatting or not having access to that random pivot table function you can't live without. It's available now in Google Play for tablets running 3.2 and higher.