Audio and Video

If you are on Windows:
Go with AirVideo (you won’t be able to stream audio files), but the quality of the h.264 playback and the HD makes up for that

If you are on a Mac
Go with StreamToMe, similar to AirVideo, its only advantage is that it can stream audio and video.

Documents
GoodReader is what you want. GoodReader is an app that enables you to connect to all kinds of file servers, be they cloud-based (Google Docs, Dropbox, or MobileMe) or local (an FTP or WebDAV server). Word, Excel, powerpoint, pdf and text documents can all be viewed via good reader