The documentation for content-types is in RFC 2046
http://www.imc.org/rfc2046

There are 7 high-level types:
text
image
audio
video
application
multipart
message

Each of these has subtypes. For example:
Text/Plain
Image/Gif
Video/Mpeg
Application/Octet-stream
Multipart/Mixed
Message/Rfc822

There are many of these, and the list keeps growing as applications
keep getting written. They are registered with IANA, according to the
procedures described in RFC 2048:

http://www.imc.org/rfc2048

The list of media-types is at:

http://www.isi.edu/in-notes/iana/assignments/media-types/media-types

I hope this helps.

Francoise