Quik.io's universal PC-to-iPad streaming service just hit the App Store, and for a limited time, the app (and service) is absolutely free. QuikIO HD allows you to stream any media file and convert it to a format viewable by the iPad. The service works by installing it on your Windows-based PC or Mac, choosing which folders you want to share, and then installing the app on your iPad.
In many ways, it is similar to the Home Sharing service offered by iTunes. But the key difference is that QuikIO isn't limited to music and movies. You can also share pictures and documents, such as your files from Word or Excel. This makes it a great way to get access to a large number of files on your PC. I would still suggest using Home Sharing for music and movies, since it interacts with your Music and Videos apps on your iPad, but for everything else (or for music and movies you have outside of iTunes), QuikIO is an excellent service.