The Audio and Video formats are created based on the codecs used. For example, the XviD codec will always allow you to create content in MPEG-4 ASP format.
The list of most used video formats is pretty big, but the most common video formats you'll encounter are: AVI, Mpeg, MKV, and AVI.
For the audio formats, the most common ones are: MP3, WAV, FLAC, OGG, and WMA.
Video formats: http://en.wikipedia.org/wiki/Video_file_format
Audio formats: http://en.wikipedia.org/wiki/Audio_file_format