Office in the cloud: CloudOn
Running Windows on an iPad can be a disconcerting experience, given how they weren't designed for each other. But the CloudOn service nicely integrates the Windows versions of Excel, PowerPoint, and Word, as well as Adobe Reader, with the iPad's native keyboard and Share facility. Plus, it uses your existing Dropbox or Box cloud storage for files, so you don't have to worry about version control across multiple devices. It has a few flaws, but when you need the full version of Microsoft Office, CloudOn is a very handy option -- as long as you have a live Internet connection, of course.